Rats are smart, trap one and good chance you won't catch another in that trap or with that bait for some time. Build a rat trap better cheaper than you can buy.
You need a small trash can 30 inches deep or so. fix a ramp up to the edge of the trash can, then fix a stout wire near the top from one side of the can to the other. Take a pop can and drill holes in each end just big enough for the wire to fit through but will allow the can to spin. Place the pop can in the middle of the wire with some tape at each end on the wire so that can will stay in the center of the trash can.
Now smear peanut butter on the pop can, put 12 to 16 inches of water in the trash can and you have a trap that will work over and over.
The rats or mice will walk up the ramp walk the wire out to the can and once on the can it will spin they will slip off and drowned in the water and the trap is always ready for the next victim.
We used to build these for mice using a 5 gallon bucket and a pop can. You might need or want to try a larger can for rats and that is why I said a trash can rather than a bucket. It needs to be deep enough so the vermin can never get out, that their feet can't reach the bottom, and have to keep swimming. I have rid the pestilence of skunks this way using a 55 gallon can too. For the skunks we would have trash floating in the water and the skunk would jump in to a sure death, and never stink.
Uuuuggghhhh! That might be worse than the time I had to burn the crap buckets in Iraq. Nasty, nasty stuff.