My dog Rex is having issues.?

Rex is a smart Border Collie/Malamute mix which normally causes no problems. Lately he has been peeing in the house and refuses to go in the back yard.

Five days ago my husband and I found a gas can in our back yard. Neither one of put it there. Ever since then Rex refuses to go in the back yard. He is an indoor dog but I guess he was out there when that happened. He is not hurt in any way but he is fearful of going in the back yard. We have tried forcing him out there (until we put 2 an 2 together) and we have tried treats. Even with us out there giving him treats he refuses to go in the grass he just stays on the cement part.

Does any one know any techniques to get him to go back out in the grass? Since then we put a lock on the gate and watch the dogs while they are outside. I love my dog but we also have 2 more so it ouldn't be fair to walk him around the neighborhood every time we put the other 2 in the back yard.

We live in a city but have a good sized back yard. The dogs are only outside when we are home. There was no signs of gas in the can or poured around or house or our dog. We live in a quiet neighborhood so this is a fluke.

Three weeks ago I had a miscarriage so he was staying away from me and acting out once in a while. This is why it took us a while to think something happend to him when we found the gas can in the back yard.