My Rocky, is a mutt/sharpei/american bulldog/pound puppy. up until yesterday keeping a collar on him all the time wasnt a big deal. he was rarely outside alone. but i put up a fence and now he's got this big yard to run in. but i want him to have a collar on in case he escapes. But my problem is that his neck is quite a bit bigger than his neck. so any collar i put on him falls off. so i'm thinking of a harness, tho he's 11 years old and never had one. but is that something i can leave on him all the time like i would a collar? are there any drawbacks of using a harness with a big ole 80lb dog?