The number 1 rule is DON'T SET THE HOOK. Wait until your line is swimming away. Your fish will be in the mouth every time.

The problem is you have an unnaturally high density of fish in a ditch. You can snag them with any method including float fishing. The problem is not only intentional snagging, you will accidentally snag fish constantly unless you have a lot of patience and wait for your line to swim away.