I think you need leader to act as a shock absorber, especially while trolling. I think thats why most trolling setups are full mono

 If running braid main line then Bimini twist to 100lb wind on leader, then tie a good quality snap swivel (SS richter or similar) to the end of that. Also make sure your drag isn't set too tight while trolling, you just want enough to set the hooks and not rip them out the fishs mouth.

maybe you had a dud batch of flurocarbon?

I go braid - (bimini-GT knot) 2or300lb mono wind on (4-5m) - (3 turn Uni knot or crimp) 200lb Richter clip swivel. Then clip on whatever you like.

If mainly chasing Bills it's not a bad idea to ad an extra 50m topshot in to add some more stretch, or just run mono

I think running a longer mono leader might be the answer. If you're happy to tie FG knots then you can comfortably wind 5-10m on, then go to wire trace. assuming your knots are all good, sometimes a short mono leader will not absorb enough of the initial strike and can result in pinging lines or pulled hooks.

maybe also look at what drag you're running, if too much drag this can also result in unnecessary bust offs.24kg braid probably has a higher breaking strain than 60lb fluro. as you probably know, try to stick to no more than 1/3rd breaking strain rule of thumb for drag setting.

Might need to reassess the knot used. Easier to tie knots with mono than fluoro, fluoro has bugger all stretch. Should 'bench test' your knots too

its[unless its faulty] the knot I reakon, unless its shit line not a fan of big clips, help kill the action of the lure, rather troll mono, although have caught many fish on braid trolling, your not using a docker knot by any chance ha ha

 I go the same as Matt Miller but I use mono the whole way through. 40lb mainline and 80-100lb wind on leader using a bimini. Straight to a richter clip swivel but I use a thumb knot for this as it's self tightning. I've never lost a fish to knot failure only the line giving in after having been monstered by a huge Marlin for 45mins.

 I have Used braid straight to wire many times especially at dhi trawling around I've   never had a problem with hookups  the trick is in drag set up 

what was the track like up through steep get much rain?

Never used or wanted to know how to tie a leader on and hardly ever lost a fish at the side of the boat.
Always tied the main line directly to the swivel when using wire or to the lure itself.

Sounds like the line you had trouble with is either stretched or sun damaged and should have been stripped off, probably the top 20-30 metres at least or you were using the wrong knot.

I may get crucified for these comments but I think the old 'don't use braid for trolling' train of thought originated when the new at the time (some time ago now) carbon graphite rods were self destructing when people were trolling with braid. The answer from the 'experts' was simply don't use braid for trolling and this mentality I think has remained with us. Remember this barrow was probably being pushed by the rod manufacturers. I think there are many positives trolling with braid but this may depend on the species you are targeting. For example tuna generally have soft mouths and there is no need for ultra sharp fine gauge hooks or non stretch lines as these may increase the chance of the hook tearing during the fight or falling out if given any slack line. Billfish on the other hand are hard mouthed and as I see it there could well be a benefit in using braid when trolling lures for them. From what I have read many bill fisherman have found the limited stretch of braid when combined with sharp hooks has increased their hook up ratios when trolling lures. Without doubt the angler has more of a safety cushion with mono and there is less margin for error with braid. I have read countless times on fishing sites that you must use a short length mono to absorb the shock when bottom bouncing with braid as the mainline. Really, be a devil and forget the mono. I guess each to their own but I wouldn't discard running all braid.
Having said all that I think the problem you experienced with the mono failing at the knot to the swivel is probably related more to bad mono or poor knots rather than anything else.

 How many times did the knot give way? Was it on strike? Are you sure it gave way? I'm just wanting to eliminate the possibility you actually had a strike on the swivel and got cut off.

all I know is I have 1 mono outfit which I troll and a couple of braid setups are used on the boat, strike hook up is about 60% on the mono against 3 other outfits, all so a pinkie on the troll on a mono this year + 2 sambos, even up north have hooked sailies and marlin on the mono, none on braid

 lol its so technical, using mono tie your mainline to a swivel, haywire twist your single strand wire to the swivel and your lure. done dont over complicate it

using braid tie an FG knot to 80lb leader no need for anything more, wind on 15 odd metres tie a swivel on it haywire twist your wire and lure on done

Tips:

buy a new roll of black magic leader cheap and effective, save your fluro carbon for whiting and bream

use a half blood knot to tie your swivels on no need for over complicated crap

make sure you can tie knots before you go fishing.

always use black swivels

always use single strand wire

never use crimps

use a light drag, no need to skull drag him in a mackeral will not spool you

When we trolled at Dirk it was 30lb braid, to 60lb mono to haywire twist and a slightly heavier setup with 80lb mono. I busted off once late in the day on a mackie on the 30lb gear just due to impatience, locked it up and h8gh stucking haha. Was surprised we didnt get sharked at all coz there were plenty of them cruising around, they were only interested in the fish we chucked back

yeah get rid of the weld wire and get someone to how you how to tie single stand wire haywire twist . Once you get the hang of it , its not difficult. Keep your wire leaders short as Mackies will find the swivel attached to the hooked fish and chew it off. I lost heaps until I worked out going longer wasn't helping. 500mm is enough.

Other thing as Beau said,It could be sharks biting you off. Or a combo of all of the things above. Once you get it sussed, you will be cool, You shouldn't be losing fish very often.

 If you want the lazy mans option go to Oceanside and get the pre-made single strand wire trace from them. I think it's called Razor haywire twist trace. It has the twist already made that you put on the lure and a ring on the other end that you clip your snap swivel on to. I picked up a few packs last august when I was in Perth and I've never had a problem with them. Apart from sharks attaching themselves to the fish I hooked. Thinking about it I need to get some more. 

 Thanks for all the input.  Was a frustrsting week on more than just the fishing front.  Wind, swell, snapped an anchor rope and lost the anchor (have the coord's in 6m if someone wants to dive for it...) lost some lures, the spare wheel bracket snapped on the way home and lost the spare wheel, and if that wasn't enough I found an old rusty broken knife blade at the campsite.... and have the sore foot, the tetnes injection and antibiotics to prove it!  But, my worst day fishing is better than my best day at work :)

 randall im heading up in 4 weeks and might be able to get it for you,couple of the blokes will be diving