ive used mk 4 fenns placed in a home made tunnel on well used runs. the tunnel is made from plywoodand has a flap in the middle on a hinge. inside the tunnel i also put in two small fences, 1 either side of the trap just leaving a 2 inch gap at the top. thrn iset the trap and leave the safty on for a few days and bait the trap with butter/i cant believe its not butter(what ever i can affoard at the time). then after a few days i take the safty off, the rats come down the tunnel, which by now they are used to, jump over the fence and land right in the middle of the fenn trap which now has the s