I use a sort of semi fixed inline running rig, something ive played around with, and which probably already exists, i came up with when playing around with a few bits and bobs. But basicaly i use an inline lead, and put a tail rubber over the swivel which connects to the hooklink, then i simply pull the lead onto the tail rubber (inner of lead is removed) very lightly. This gives it sort of a bolt rig effect, just so it pulls that hook into the bottom lip, but once a carp shakes its head a couple of time, the lead comes back off the tail rubber, which now makes it free running, making it 100% and alot harder for the carp to get the hook out of its mouth.
Hope that may help?
Ross.