Fence paint.

subjecttocontract

I've had lots of success with Cuprinol. I've a summer house that's over 20 years old that's been coated 3 times with it in that time and a couple of side gates that are 30 years old that look like new. A generous coat of Cuprinol will work on new stuff. But it's not cheap, far more expensive than water based products. You get what you pay for I guess.

Yarmy

When I got a shed a few years back, the guy I bought it from advised to always use an oil based paint/preserver. He said it would be more expensive but better than water based paints.