When installing a wooden double gate, it is important to have an additional latch or stop for the gate. If the latch shown below is the only one used, the wind will easily blow the gate open…

We recommend an additional latch and many different styles will work.
The key is to stop the gate from moving or twisting in the wind, here are several ideas….

This type of bar latch works well, especially if one side is stabilized with a device like the one shown below…

This or a variation of this device works very well, especially when there is concrete, because it stabilizes one side of the gate, then the latch has something stable to latch onto making for a gate that is less likely to blow open in moderate wind.
When there is no concrete, drive a 1/2″ piece of galvanized pipe into the ground and let the stop fall into it.

Come up with your own creative idea!! A long locking bar works probably the best but is normally only accessible from one side.
This one was shown at http://www.sfallstars.com/barn-doors-and-fence-gates-backwood-enterprise-tj4motua.html
Happy Latching!