We have kayak'd with our dogs for years.  If you are just taking your pup for a ride, then an inflatable may work, although you will want some sort of liner between their claws and your boat.  Our dogs get in and out of our boat at will and will swim boat to boat 'to check on all of us'.  A good life jacket with handle is necessary so we can assist them getting back in the boat in open water.  We actually taught our dogs to stay with us when hiking by working with them while running the shoreline and swimming between boats.  We use open recreation kayays (Prodigy, and a Wilderness tandem with seat removed, for our 95 lb labradoodle), which seem roomy and sturdy enough for the dogs and us.  We plan on kayak camping, so play time in the boats is important to teach the dogs what is safe and acceptable behavior.  Hope this helps..