That's one way to do it I suppose, tho installing a gate with the top hinge pin pointing down is the way it's normally done to prevent anything (or anyone) from just lifting the gate up off it's hinge pins for access. Whatever works tho.
Oops--I type slower than Bruce)
Agreed..the top hinge down is the "normal" way to install. I guess i've never seen "slippage" because all the gates that are used up here have the bottom straps welded onto them as greybeard mentioned, they are not a thing you clamp on...even if you did clamp it on i dont see why it would just start sliding one day and if it did why could you not just tighten it more?
I'm thinking your slippage problem could also be solved by using tall hinge posts and cross cabling them....thats what most here do for long gates of wood or metal.