Short circuit of automatic sprinkler

I have an automatic sprinkler system, and for some reason when the timer finishes, the sprinkler keeps running. It seems like a short of some kind because all I have to do to shut it off is touch the control valve for that zone with a screwdriver. What can I do about this because I cannot water the lawn when I am on vacation and having a hard time recruiting people to make sure that same thing doesn't happen. (it ran for 10 hours once when I scheduled it after I had gone to work)

Thanks for your help

Throttle down the flow control, if the valve has one. Otherwise, replace the valve, or swap out all the parts with a new valve.

Unlikely that it is a "short circuit". It is either the solenoid on the valve sticking open, or the diaphragm on the valve sticking open. Get a new solenoid, and a valve overhaul kit.

Same thing happened to me recently. Like Jimbo said - a new solenoid fixed it. Turn off the water and the power to the timer, disconnect the wires, and unscrew the solenoid to remove. A new one cost about $6 at HD.