Does it hurt a dog to wear a harness all the time?
Technically, a dog can wear a harness most of the time, but there are some exceptions. For example, it's best (and more comfortable for your dog) to remove the harness at night. Also, if your dog has long hair, then keeping the harness on for extended periods could lead to tangles and matted fur.

Can a dog wear a collar and a harness at the same time?
The short answer is: Yes, You can use both restraints on your dog, especially if you want to have absolute control over your pup. Dog owners who put both accessories on their dogs at the same time often use the collar to keep licenses and ID tags and the harness to have better control of their dogs' movements.