I usually look for someone camped by the takeout spot I'm coming from (mainly Yakima R.) and ask them to watch the boat while I go to pickup my rig. 9 times out of 10 they'll also offer a ride to my rig, an added benefit. I understand that won't work all the time so I use a cable chain through the frame, pontoon loops, and around a tree also.
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Mark Strand
aka - TC