As PennyB said, a really solid 'leave it' command. Amber will also spit things out if I ask her to leave it - its worth practising using high value treats (pieces of ham / cheese). We used to leave toys around (bought for 20p from car boot sales) and practised leave it with those....
I'm not sure how old Ringo is, but I really wouldn't beat yourself up about it. He did leave it (albeit a bit late) and sometimes, despite your best efforts, things don't go to plan. I do remember an awful walk on the (usually deserted) golf course when Archie stole someone's golf ball and wouldn't give back for anything!