IM a roofer and from what ive seen the best vents for animal protection are sloped vents. IT Has an opening for air on the front and no Lip on the back. You Can get them at most roofing supply stores, avoid home depot or RONA. The old style steel ones are garbage A heavy rain storm can dent them, plastic roof vents are alot more durable. Wire mesh under the vents will keep them out but then you still have a broken vent to deal with. If one does get in your attic make sure she didn't leave babies behind. Once you seal up the access point she will rip your soffits , roof anything she can find to get her babies. IF there is babies put them in a shoebox with insulation from the attic and put it on the ground close to where the access points was. Within an hour or so mother will have collected her babies