I have always found that sprinkling some ajax or comet at their point of entry always works well, although not permanent, (the need to reapply is required every so often). And it's very likely that that just may force them to find another entrance elsewhere.
If you can, try to follow their path backward to the point of entry. Apply a dry sprinkle of the powder there, and perhaps on the outside of entry, (so long as you have an idea where they are entering from).

Since you reside in an apartment, perhaps complain to the landlord to have this problem corrected?

Hope that helps some...

Shangrala
:Smile: