Your dog will chew them up. They will get hung up in trees. You will drive away from your training grounds and forget them. You'll throw them directly into intergalactic worm holes to another dimension disguised as cover. You'll have floating bumpers that immediately sink. After you throw a mark for your dog at a public park, some random, unleashed mutt will invariably grab your bumper and run like hell the other way. I have done all of these things and more, because the first rule of retriever club is: your bumpers don't like you and will always try to escape.