Axiom subs have a grill over the ports. Keeps out toys, milk bottles and small rodents.

If that's not enough, the SVS tower subs have a METAL grill over the ports which will keep out larger rodents as well

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8