I got this one from a guide - use a hockey stick shaft. Wrap a handle of paracord and but a bolt in the end so it doesn't break hitting rocks. Drill a hold in the handle and attach a lanyard with a carabiner clip so you clip it to your vest, wading belt, etc. Floats downstream when not in use and supports by ample rump quite well.

However, I made a new one a couple of summers ago - using a broom closet pole. I made it shoulder height so it goes into deeper holes and I have plenty above the waterline to leverage with.

Truly works great and cost just a couple of bucks. Use sandpaper to round over the top and bottom edge - and the paracord handle makes a great grip even when wet.