Post of the following signs at each potential point-of-entry.

Dear Mr. Butcher, starting tomorrow, please leave eight pounds of meat
for Brutus. Six pounds only makes him angry and vicious!

Dear Mr. Mailman, we found bloodstains all over our mail. They must be
yours. The next time you put mail into our slot, please be sure to keep
all parts of your body well clear of all openings. P.S. - Any sign of
that book we sent for, "The Care and Feeding of Wild Jungle Cats"?
Thanks Mr. Roy

Selma, don't come in! The boa constrictor got loose again...