There are two reasons why a sprinkler will leak water when the system is supposed to be off.
The solution is to install check valves, such as the HCV, on sprinklers and lateral lines.
Hunter sprinklers are also able to have check valves added in the field after they are installed.
If the zone valve for that particular station is diagnosed as the problem then the solution is:
You may need to replace the diaphragm assembly if there is visible damage.