Use them on reef/rock otherwise use a plough type for weed and sand.

Need proper weight/size for the boat and enough chain.
Shackle chain to prong end of anchor (wire through shackle to stop it coming undone) and then run chain down the shaft and put a good quality heavy duty cable tie through the chain and other end. carry spare cable ties.

When the anchor gets stuck you can most times break the cable tie and pull the anchor out backwards. Sometimes its the chain gets wrapped around something solid and then you can only cut the rope and save what you can.

Lowering chain straight to lay out rather than dumping the lot in a heap equals less chance of chain getting wrapped round a rock

Very interested in this post as well. Have been wondering wether I have been using mine correctly after being pretty stuck a few times. Will try the shackle to prong end and cable tie. Thanks Paul for the advice

 I find that I have the prongs bent at 70 to 80 degrees works well for easy release.

 Thanks for your advice Paul.What size anchour and how much chain would you recommend for a 5.9m glass boat?