One step ahead does have a website but I'm not sure of the address. You can probably find it with a search. My son isn't a wanderer but this is what we did:
1) Anytime there were crowds he was either in his stroller. If he wasn't in the stroller he had to have a hand or be carried. NO exceptions. He knew this and didn't have a problem.
2) If he wanted to walk he had to either have a hand on the stoller or have the hand of an adult. Again, we made it clear NO exceptions. When he didn't, we put him right back in the stroller ... only took once for him to get the message.
The crowds did overwhelm him, when it was crowded. He tended to stay very close. But, our son has always done that so we haven't had that problem.
Some have suggested putting his name, your hotel, and a cell number pinned inside the shirt. They say a good place is the tag in the back of the shirt.
Also, we introduce our son to a CM when we enter the park. We point out the name tag and tell him to find someone with a nametag like that. Then as we go by a store, we stroll in, introduce him to the CM and remind him that if he can't see mommy and daddy he needs to find someone with a name tag like that.
The fanny pack would be a great idea but my son wouldn't probably wear it. Good luck. I know it can make you crazy thinking of all the possibilities. But it typically is never as bad as we imagine it, right?