Why does my outdoor garden faucet drip?

It's not a drop that comes from the nozzle, but from a pinhole that is on the valve. I think it's sort of a failsafe to help protect if my pipes freeze, but is there a way to override this? I want to run my garden on a timer which means I would need to have my valve turned on 24/7 (at least when I'm not on vacation and want to water my lawn)