I went with the exact stiff arm and cable system show in the photo. The only difference is my dock is a 30 foot covered pontoon boat. I used 20 ft sections of galvanized pipe and welded automotive tie rod ends on each end to give it some pivet room. I put turnbuckls on the 2 cables. Have had no problems with mine at all for several years now. If you wanted to beef up the galvanized pipe more, you could put rebar inside of it before welding the tierod ends on. Mine does not flex at all so I didn't use rebar. I screwed mobile home augers in the ground and attached the tie rods to them.

Dear Alcohol, We had a deal where you would make me funnier, smarter, and a better dancer... I saw the video... We need to talk.