These tips come from 5 years of trapping. They are a formidable enemy, but they have their weaknesses. Peanut butter seems to be "squirrel crack" - they just can't get enough. I probably never would have known to use only one trap door on the Havahart unless I had actually seen them "bolt thru" on camera. The peanut butter is so effective it's almost unfair to the little buggers. When I went to the two-cup method, my success rate just about doubled. Apparently grabbing the first "free" cup just inside the trap overwhelms their sense of fear and they usually circle the trap once and then go right down the chute.
If my experience is any guide, the next family won't move in until this one is long gone. The invade the fringes of each other's territory rather than pull "storm the castle" raids. Just when I think I've cleared the area, juvenile males from nearby areas begin to filter in, looking to stake a territory for themselves.
One you've removed the current family, keep the trap baited and ready for any straggler - and remember to check it every couple of days. Squirrels are like goats. They smell bad enough when they are alive but *really* bad after a little rotting sets in. I wouldn't use poison for that reason. The stink is pretty awful. DAMHIKT.
I would estimate that there were 10 times the number of squirrels that I thought there were. They have foraging patterns and they all work the fringes of other squirrel clan's territories. They are highly active on trash day because of all the spilled food and disturbed garbage cans. There are a lot more around that you can imagine, of that I am sure. (-:
That model Havahart takes a pretty big tank to immerse completely and the death is not slow or peaceful by any means. That's why I use a stun-gun. With an accurate first hit, there's not a sound or any thrashing at all. They go stiff and a few seconds later it's all over. You can get a serviceable unit for $25 on Amazon that had a flashlight built-in. I used to bag them tightly and use automobile starting fluid in a can (mostly ether) to knock them out and transfer them to a smaller holding cage I had for guinea pigs (it took ten minutes for the squirrel to chew through). My wife was afraid that the odd smell of ether would make our neighbors think we were running a meth lab, so that method was abandoned.
That's usually people's first reaction. There was a great article in the NY Times' gardening section that talked about how quickly that benevolent attitude can change. Destruction of a prized garden, demolishment of the interior of a house (one squirrel did thousands of $'s worth of damage after being trapped for a week when I was away) and in my case, chewing its way out of a wire cage and burlap to then climb onto my head during a relocation drive ended all such attempts. The article described former "tree huggers" and little old ladies whose attitudes changed mightily when something they loved was destroyed by rodents or other garden pests.
One time, I accidentally caught a possum and made the mistake of taking it inside the house in the trap. It spooged the floor with the nastiest green schmutz I've ever smelled. I no longer leave the traps out overnight. I had one raccoon try to drag the whole damn trap off the porch. This was the same raccoon that left a package of meat on my car. At first I thought someone was sending me a death threat (as in you're dead meat) but my neighbor said she had startled a raccoon raiding her trash and he was running off with huge load of meat that was freezer-burned.
Good luck. I don't know how you transport the little buggers but if it's in your car I recommend using the magnets to keep that U shaped lock wire down. I also suggest putting the entire trap inside a plastic bag since a large male squirrel can spray some pretty nasty and VERY persistent yuck in your car. The one thing you don't want is a panicked rodent running around inside your car while you're driving.
-- Bobby G.