Rodent control with wax-opener vent?

[tropterrarium]

How do you keep rodents out of a GH with a lower vent that is operated by an automatic wax opener (gigavent)?

- I cannot put stiff fine mesh metal screen in, because the arm of the auto vent opener would interfere, or the slot in it would be so large that any rat could easily get through it.

- Been thinking about nylon fabric that is attached to outside frame and window, forming an expandable bag. But rodents will easily chew through any plastic.

- Tried to find fine-mesh flexible fabric. Smallest hole I can find is 2x2 cm (0.8x0.8") which may still be too large for rats, and only found bulk supplier for zoo aviaries.

Any other obvious options I've overlooked?