Outdoor Gate Alarm Contacts?

I have a back fire exit walkway behind our building. At the end I have a gate with a pushbar so they can get out. I need to put a alarm contact on the gate and hook it to the existing axis camera thats on the gate to get less false motion alarms. Any recommendations? Its a salt water bay enviroment also.

what about heavy duty ss door contacts or mechanical door contact???

I have called three different iron gate fabricators this morning to find out which type of contacts they install (and warranty) in factory units. I'll update with their feedback!

Any wide gap contact like the one above or below will fit the bill.