Hey Sammy ...
Try this link: Web Master
I know someone who had the SAME PROBLEM and this worked perfectly. Dog was a sheppard mix who was too smart for his own good. He broke a tooth trying to escape his crate so that did not work. Not only did he get out of a regular harness, but also escaped a fully fenced yard.
So he was safely tied out with the above harness during the day within reach of his dog house, food and water. They also had to use vinyl covered metal cable to tie him out as he chewed through rope too. Metal cable makes it harder for the dog to entangle itself, but Shammy is so right ... make sure there are no trees, shrubs, fences, posts ... anything ... he can get caught up on. Once that happens he will stuggle to get free and hurt himself ... or much much worse. He should be able to get to his dog house and go inside it ... but not around it.
If he has to be outside, a run is safest but expesnive.