Stealing others dogs balls/toys

Hi all, it’s been a while since I’ve posted and my pup is 12 months now. Some things have improved, but people generally still describe Charlie as “a lot”. Even my friend who looks after people’s dogs all year round considers Charlie as a “special little energiser bunny” who is “more work than a lot of dogs”. Anyway… that’s just for context.

We don’t take him to the dog park anymore for various reasons associated with naughtiness, but we do take him for off lead time in this huge run area where you maybe see a dog every 200 metres or so (it’s about 2kms in length). Charlie is friendly, and LOVES other people and dogs, but he has this awful habit of stealing other dogs balls (he hates balls himself) and we cannot for the life of us (and the other poor owners, AND the other dogs) get it off him once he has it. It’s a huge game to him because he only does it BECAUSE of the dogs chasing him that he loves (and he’s so fast). Treats don’t work, calling doesn’t work. Ignoring him doesn’t work. We have all just walked away on many occasions and ignored the hell out of him for 15 minutes and he just sits with the ball – he is the most stubborn dog. People get so angry with us. We eventually only manage it by somehow catching him, or throwing high quality treats away from him and eventually he just can’t hold both the treats and the ball in his mouth at the same time. It is so embarrassing. Worst part is that he actually knows the command “drop it” and “leave it” and will listen if it’s not something he wants much anyway. Charlie will literally only do the command if he wants to (and this applies to EVERYTHING).

Is this all because he is still young? Do I just ban off-lead time altogether? Is it his personality? He also has a habit of crouching down and pouncing on other dogs which is a whole other level of worry 😩. Just looking for some advice (please no judgement as this forum can be mixed). It may be that off-leash is just a no-go for Charlie and I guess I’d be ok with that..