...I got a screen top and the walls of their enclosure is too high for anything else to get in at them...
Doesn't matter- wild rodents carry all sorts of diseases that transfer thru screen tops etc- plus fleas, mites, etc. Don't breed rodents in a shed where there's ANY access by wild rodents. The diseases they catch (or just carry) can also infect YOU.
Rudeness is the weak man's imitation of strength. Eric Hoffer(1902 - 1983)
“The greatness of a nation and its moral progress can be judged by the way its animals are treated.” ~ Gandhi