No harness is "escape proof". In most cases when a dog is able to slip out of a harness it is because the harness does not fit the dog properly or it is not the proper style for that dog.

Not all dogs can wear all styles. It is important when selecting a harness that it fits the dog properly.

To check for size you should be able to slip two fingers between the harness and the dog's body to confirm proper fit. When inside, try pulling the harness forward over the dog's head. If you are able to pull it off, the dog will be able to back out of it as well. Also, when out on a walk and your dog starts to pull backwards, pull straight up on the harness, so that your leash is vertical, this will prevent the harness from being pulled over the head. 

That being said, we do recommend step-in style harnesses for escape artists. Some good options would be the Buddy-Belt harnesses, NYD Step-In harnesses, Dogo EasyGo harnesses, or the Puppia Vest Harness B.