You can get a mighty Mule or a bulldog gate lock, both of which are weatherproof and which have their own control systems. Then you can add a Z wave relay, typically a mimolite, to jumpstart the lock’s control. It works fine, it’s just that you have to get multiple devices to make everything work with smartthings. 
Here’s a good project report from one guy who did it:
Also, many gate locks which have a button remote for use inside the house can be activated with a switchbot.
2019 Switchbot Review ( robot button pusher), integration through IFTTT
So basically find a lock which already has an electronic control system, and then integrate to the control system rather than to the lock itself. it’s hacky, but it works.