I would consider 2 options to try and combat the problem and lower the population at best. First, many gardeners use fox urine to keep rabbits and other animals away from their gardens, this also works for rats. They will avoid the smell of fox urine at all costs since it's a predator. Now, the bad part is for the first few days it will smell like urine, but spray it along your property line and housing line. Second, start putting out bait to kill the rats, some decon pellets wrapped in cookie dough will do the trick, especially if you see them so often. The cookie dough will slow down the rats metabolism and allow the poison to sit in the system longer and have mother rats milk-feed the babies the poison before dying off. Best of luck.