@flowertop,
Without having defined rules, there are none to break. However, you should
check with city ordinances to see if you're in violation, otherwise your landlord
doesn't have a leg to stand on. Nonetheless, try to talk to him and reason with him. A guard dog keeps away people on the prowl.
Check around in the neighborhood, if any of your other neighbors have pets.
If they do, there is your answer.