Reddit mentions of Stanley Hardware S760-828 1273 Anti-Sag Gate Kits in

Looks great. At some point, your gate will sag. When that happens, install one of these to fix it permanently http://www.amazon.com/Stanley-Hardware-76-0828-Anti-Sag-Gate/dp/B00004Z109/ref=sr_1_11?ie=UTF8&qid=1398628557&sr=8-11&keywords=gate+kit

Honestly, they will all do the job. The problem is your gate, not the lock. You need to use use brackets:

https://www.homedepot.com/p/Homax-EasyGate-No-Sag-Gate-Bracket-Kit-2614/100020199

or a tension rods and a turnbuckle:

https://www.amazon.com/Stanley-Hardware-S760-828-1273-Anti-Sag/dp/B00004Z109

Once you do that, you can use any of those latches with confidence. You might also consider replacing the hinges with a spring loaded self closing feature. Will cut down a lot on the banging:

https://www.amazon.com/Closing-2-Pack-Finish-Adjustable-Dragging/dp/B00NETPZN6