The one's I have dealt with in this populous city (in which dogs are on leashed and walked by owners but not to get rats) are smart enough to avoid traps once one gets caught in them. Poison works best, but there are different types, and some require a PCO license. I found
this works better than the constant fed types. It is best to pulverize blocks and mix them about 5 parts poison to 1 part peanut butter, put in sandwich bags and place them where cats and kids cannot get into. Squirrel population decreases also.
The country solution is a large bucket with a baited roller that spins and dumps the little sobs into water they cannot leap out of (certain depth works), and they swim around until they drown. Very efficient as you say.