You should get them a puppy life vest. They likely won't enjoy wearing one the first couple times out but my retriever, Buster, doesn't mind it at all anymore. Dogs really aren't smart enough to come back to shore when they have had enough so they will push themselves past the point of exhaustion and sink. Plus, with the bright colors the vests come in, it improves their visibility to people and nearby boaters, and it'll give them the opportunity to actually swim instead of just walking around in the water
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My wife is a real estate agent in the lakes region and central NH primarily--shoot me a message if you don't already have an agent working on your behalf!