I trap a lot of ferals...most are trap shy.
I set up one of these...with a secured top. Drive a railroad spike or 1 inch rebar into the ground where the door meets the frame-tie a looooong piece of rope to the center of the door (one the door frame, where it meets the frame of the kennel)
Feed for 48 hours with the door tied completely open so that it doesn't move in the wind. On day 3, game on. They walk in to eat, I'm about 25 yards off in my truck, yank that rope, the bottom of the door hits the rebar-and stops it dead right there as if it was locked. The dog usually bounces around in there for a couple of minutes, once they realize they can't get out. Tie off the rope firmly on the truck end, grab a catch pole, don't un-tie the door end of the rope until you can physically close the door-get in there when you're ready...and collar the dog.
They're quick to put together, and quick to take apart, fit in the back of a pickup truck-just make dang sure you reinforce the bottom and top and sides of the chain link to the frame using heavy wire...really ticked off dogs will try to push out through anywhere they can, and make some type of a top out of welded wire fencing...it just needs to sit up on top with a few bungee cords holding it down. http://www.amazon.com/Lucky-Dog-Galvaniz...;s=pet-supplies
Here's pics of a Whippet mix that had been running for 18 months. Would not commit to a trap even though she was literally starving to death. This is exactly how I got her.
Look at the second to last pic. That's her head trying to go through the chain link once she realized she was trapped. That's why you want to reinforce the chain link against the frame with heavy wire, top and bottom. Some dogs are strong enough to go through it if you don't.
Last pic is 6 months later, going to her forever home. :-)