Foxes are breaking into rabbits cage?

You're quite lucky that the rabbits are alive. You could try setting live traps in an attempt to relocate or dispose of the foxes. They will kill the rabbits given the chance, we've lost tons of chickens and ducks to foxes in the past. Sounds like you need to get new cages and keep locks or some kind of extra latches on the doors. Place them up higher off of the ground so that the cages are less likely to be broken into. Do you have some kind of shed or garage you could possibly put them in?