To train a dog to accept a dog run or crate, you have to make the experience as pleasant as possible. Try feeding the dog in there without closing the door until the dog goes in willingly. If the dog won't even go in the pen for his favorite food, then start by feeding the dog next to the run (as close to it as possible) and over time moving the food closer and closer to the door and finally into the pen. Once the dog is going in there willingly to eat, close the door briefly, but let the dog out when it finishes eating. Over time, you can gradually enclose the dog for longer time periods, but the trick is to go slowly. If you go too fast, you will be back to square one. It can also help to give him a treat or toy (like a chew bone or stuffed kong toy) that he doesn't normally get and will take a while to eat. Buster cubes (those toys you put treats in that the dog has to play with to get the treats out) are good too, because they can keep a dog busy for a while. The trick is to make the dog associate the enclosure with something good. Once the dog gets used to the run, it is important not to expect the dog to stay in there for excessive time periods (more than a few hours a day) and make sure the dog has plenty of exercise, socialization and family time. Like a play pen/crib for kids, a crate or dog run can be a great way to keep a dog safe when you can't supervise closely, but is harmful if you over-use it. Dogs who spend too much time cooped up in a run can actually become territorial and develop bad habits. Try to put the run somewhere where no one can tease the dog when it is in it.