Ive not tried this but: How to catch a mouse without a mousetrap ive used marsbar in the past, they seam to like it. (i hear cheese give them diarrhoea and they sometimes get the bait without getting caught -hence peanut butter marsbar etc)
Traps are the best way to go - you know exactly where the dead rat/mouse is. As I've mentioned on Tony's squirrel post, they usually die somewhere innaccessible and then smell pretty bad.
Try B&Q for rat traps (like mouse traps but bigger).
Or if you wan't to do a few at a time try a monarch