My experience with rats:
Wen i lived in Baltimore it was nearly impossible to get rid of them. I got those big rat traps and killed off a few big ones. Didn't see them for a while until my house got broken into and then I moved. Baltimore is a cesspool of poverty, crime, rats and rateros (for my hispanic friends haha).
My house now in texas has a rear fence-line shared with the neighbors for long stretches that rats like to frequent. Occasionally one will slip through the emergency drain line for the water heater. I put a trap right next to it, killed 2-3 and haven't had problems since.
Seal up any holes into your house, including eaves and overhangs, even the small ones. Clean up, lets face it, rats come into your house to eat stuff....
Outside, if you have any piles of weeds, or piles of ANYTHING rats like to make their homes in those, so clean up outside too. If they have no place to nest, no place to eat, and no place to get in your house, chances are you wont have problems anymore. That is, after you kill off the ones there. Big *** rat traps. They look like giant mouse traps. The really big rats will not be able to break free from the trap and it may not kill them for a few minutes, so make sure to stake it down or tie a little chain to it as they can crawl off leaving a bloody mess.