My suggestion is to build a couple bathouses under the eaves of your house. You can't go wrong having some bats around to eat mosquitoes and such. Lucky dog, you!
Try placing the houses near the entry that the bats are using, then put some heavy guage metal net material over the hole. You probably shouldn't block it with a solid material since it is probably there to vent moisture from your attic.
Check out the bat house project here:
http://www.batcon.org/bhra/index.html