I made myself several live catch traps based on or around the Monarch rat trap really quite easy to knock up out of half inch monoweld and a bit of garden wire. the beauty of these is you can get multiple catches, (especially young rats) you know exactly where you stand as to what is being killed and what isn't and the traps last for years...the only problem is they are not for the squeamish.
D.B.
One thing to consider for anyone who is considering using live capture traps for rats is what to do if you catch any?
Drowning is a definate no-no as it is illegal and if prosecuted will land you with a hefty fine at best (Wild Mammals Protection Act)
Releasing the 'detainees' - All you are doing is moving the problem somewhere else, they may well just come right back to you....
If you do not have the means to humanely dispatch the quarry then do not set the trap.