Any time I've taken dog's swimming I usualy have a 20 foot leash and with the little guys I put them on a harness so that if the something should happen I can get hold of them and "fish' them out of the water without hurting them. With my friend's wolfhound we just had her on a collar and a long line at the river and the water really isnt very deep. For the whippets we put a life jacket on them, really more for our entertainment than their safetly but it did help when the wolfie led us into deeper water and the little whippet's legs couldn't touch bottom. Lifejackets also make a great way to grab hold of a dog, again, just in case.
Oh and of course the ever important CAMERA!!
