Question : Problem: automatic proxy

In our company we have laptopusers.
If they logged on the network our GPO forces the proxy on.
If they are working at home, the proxy is still marked on, how can we fix this, when the laptops shutdown that the proxy is not marked anymore ???
Already tested with shutdown script+loggoff script, but it doesn't work.
Any suggestions.
Hoping soon hearing from anyone.
MUST BE FULL AUTOMATIC SO THE USERS DON'T MUST HIT A BAT FILE OR REG TO WORK AT HOME

Answer : Problem: automatic proxy

make proxy.pac file