Rumbled
I don't really want to lose him, honest!! What I do at present (and have done since he could crawl) is attach a home made luggage tag to a belt loop (used to be attached to his reins) wih the relevant information.
I have since made him a special Bongo tag with the picture on our avatar on it as well as my contact details and registration number. The reason we've got the duck on the flagpole is purely for the boy's benefit. Narrows it down, although I don't suppose our duck windsock is the only one that's ever been sold in the entire history of novelty windsocks. I use it on the beach as well (OK, so no ID with him if he's got his trunks on, but at least he knows to look for the duck).
The home made luggage tag is basically a business card which has been laminated. He usually has another card in his rucksack and another in his coat pocket.
Just remembered, if we are going anywhere busy, I always take a photo of him before we set off so that I have with me a picture of him wearing whatever he is wearing that day in case he does decide to go off on one of his expeditions
