Don't kill the snakes you find! And as mentioned above, encourage the owls, etc.
In the wild, you just have to factor in some loss. So, if you need seed from 120 plants each year, have 200 plants growing! That will allow for some predation of the seed - be it rodents, birds, etc.
I do put out some snap traps, mainly to see what is out there. Don't really use them as a control method. I'm more concerned with poachers, but haven't been able to find any human sized snap traps...