Uh.. well I have about 40 breeder rats in my basement and I have NEVER seen an outside rat. I don't think you'd have to worry about wild rats coming in.

Get good cages and you won't have an escapee. Good wire cages, or even better, lab style cages.. get em here: http://www.bigappleherp.com/bigapple...roducts/110100

Rats are super nice.. I like having them around.. but mice are disgusting.