Looking for an auger to dig pockets in river banks. 4-6 inch diameter. Durable. What do yall use?

Most durable would be a one human powered tile spade

Tile spade

My favorite if you've got no rock to deal with. Slam it in, rotate, extract . . . there ya go! One of the early Trapper Art's pocket shovels. The later ones had a shorter snout.

I've never used one, but I remember seeing a video somewhere where a guy used a 3 or 4 inch bit with an old hand powered drill.
In a lot of places on my line I will often just kick a hole in the bank.

A 4-6 inch auger is very large.