It is semi-permanent - meaning that it does have wheels enabling it to be moved; however it does have a bottom frame that is made of 2x4 boards. The frame boards form about a 3" inner lip. Would that be enough of a deterrent for predators to dig under? We are very open to any suggestions.
We are using hardware cloth on the bottom of ours, all the way around, as well as cement blocks around the edges. Many people suggest placing hardware cloth 12 inches down in the ground at an angle around the entire structure to prevent raccoons, fox, other animals from getting in. We have fox, racoons, and all other sorts of predators, so we opted to use a hardware cloth bottom for the structure and when we are home they will free range in a fenced in area.