Here is a pic of African Teak that I used a marine varnish on. I used two coats. Does not get much foot traffic, but the water from the sprinklers and from the hose did a number on it! I even coated the back! It said to do 3 coats. Maybe I should have! The varnish is peeling and the wood is warped. I knew it would happen. So as long as yours is protected, the marine varnish should be fine. That varnish will also prevent the teak from oxidizing to the natural gray color.

btw, I used Sikkens. But you may be able to use some type of top coat for exterior wood. Maybe Waterlox or something along those lines? Either way, you will have to do touch-ups once a year.