Oh, I never thought about rats. I guess those sound plausible as well.
If you have any local pets, I would not go with any kind of poison...or snap-trap.
It would be best probably, to use one of those types that are contained so that Only the rats can get in.
However, try the fence first. This way, if it is rabbits, you will know and can avoid the snakes, terriers, traps, etc. .