Throw Over Gate Loop - latch two gates that meet in the middle of an opening $37- $47
gate lock
Gate Locks - Locks for Wooden Gates
Wooden door knobs & latches
Deck Closure Option - easily slides to open  close.  Great if you have pets (not  approved for use as a child gate) or if you're tired of fighting with a latch. This post has building plans available for purchase - I pinned it because this is such a brilliant idea!
Yard Lock is a keyless wood gate lock kit that will lock and unlock a wooden gate from either side. Secure, convenient, and improves security for your yard. Dependable in extreme weather. No lost or broken keys, no frozen and rusted locks. No electronics or batteries required.
Keyless Gate Lock Lockey M220 Surface Mount Single Sided Mechanical
Gate lock for the too smart Jericho - baby gate @ top and bottom of deck steps
Pool Fences 167851: Magna Latch Child Safety Gate Lock Pool Ndpa Model Mltps2ru Professional Grade -> BUY IT NOW ONLY: $69.99 on eBay!