Thanks for your replys guys!
Seems that its something that happens to many people with a young or new dog. We haven't went back to the field yet, so don't know what will happen next time.
I think I should find out who owns the field first and ask if its ok to go back. I don't want anyone calling the farmer, or the cops, to say I'm a poacher or something!!
I would like to stay within the law.