What do when you have a dog that constantly gets its collar off?

We have a medium-large sized dog. We live near a busy road and our yard is not fenced. We rent so fencing isn't an option. We can't let the dog roam free because she's about been hit by cars several times now. We don't want to do the chaining to a dog house and her never being able to move much thing. So we put up a run. She gets to run a long way (about 150 feet plus the reach of the chain to the sides) but she is still chained. Here's the problem. That dog can get a collar off quickly. No matter how tightly we put it on. We have tried leather, nylon, and chokers. And she can also get a harness off even the kind that tighten up under the legs if the dog pulls. She backs up somehow and manages to pop both things over her head. We have built her a dog lot but she can scale the 5 foot high fence. I watched her do it. We even tried a strand of barbed wire around the top of the fence just to deter her. It didn't help. She got out anyway. Any suggestions? We do let her run every day and be with the family but when we are not outside I can't let her roam the neighborhood and risk her getting killed by a car or even the remote possibility of her hurting someone. Thanks.