Need some advice please on behavior with other dogs

Hello every one Harley is nearly coming up to 2 and from about 18 months we have noticed a change in his behavior with meeting dogs.
Its not at the point where he cannot be off the lead but I am worried it could escalate to this and want to make sure I am doing the right thing.
So when Harley is on the lead he will become unsure of dogs if they run up to him, his ears go back and tail up and some times hes stiff and his eyes go wide like he is unsure this only happens if I stand longer than a few seconds. If I am walking past I've been letting him have a quick sniff of the dogs nose and carrying on then giving him a treat. Is this the best thing to do?

Off lead he mixes with dogs much better and we always have a long lead trailing if anything were to happen suddenly, recently I've noticed he does not like packs of dogs and can get quite defensive luckily each time I've managed to get hold of him by the harness. No harm done mostly noise but it still worries me.
He will however be off lead with his ball most days and ignore mostly all dogs and if he does go over for a sniff all I have to say is "wheres your ball" and he flies back to me.

Me and my partner decided to take Harley to an indoor dog park so he could have a good run around off the lead and keep his socialisation going and for the first few times he was fine and played with lots of different dogs without incident and took a liking to a doberman and played quite rough with him all was fine until and Jack Russel and a golden retriever came over they were in a pack and the Jack Russel tried to hump Harley so the man picked him up and then out of the blue Harley jumped on the retriever and was growling and hackles up. It was quite scary but we were able again to grab him by the harness and no harm done.
so my question is do you think I should continue to take him there to socialise or not? It seems that he gets on with 90% most dogs off the lead but there are one or two he doesn't like and if challenged he does react which makes me question is it worth the risk?. I just want what best for him and would like to protect him. I've thought about just letting him socialise when his ball is in play but he doesn't see many dogs and I am worried that wouldn't be enough for him.

Any advice would be greatly appreciated sorry for the long winded post.

beth keeping up his socialisation is very important the more you do it the easier it will be . take treats with you when you see the packs of dogs id use the treats and a calm voice harley will associate the pack of dogs eventually positvely . hes at an age hes testing the boundaries with you and the other dogs . you are correcting him when hes getting out of hand and thats important too. harley is fine with one or 2 dogs it seems but finding loads hard. so yes id continue to take him where you go for walks.

I'm pretty sure that what happened with the JRT and retriever was nothing to stress much over, but to be aware of. I would say that a) Harley was already a bit excited because he was playing with others (normal), then his stress would have gone up a bit because the JRT was being bloody rude and humping him, and then to tip him over the edge this same JRT was suddenly elevated above his head, which can be very provoking for some dogs. Harley's reaction was then to redirect at the retriever.

What I would, then, be aware of is that Harley doesn't cope well with dogs being picked up near him. We had the same with Chaos and I trained him to sit, first using a squeaky toy and then using a small, well behaved dog.

I do love to see dogs running round together but I also think that these high energy situations, with various dogs who know each other only slightly, in an indoor situation, is actually asking for trouble. I took Chaos to some indoor classes, structured but still quite intense, and his ability to deal with other dogs plumetted as a result, it was just too stressful. I really regret doing it now.

I would absolutely keep up socialising but in lower key environments. Can you, for example, get the number of the owner of the dobe he liked?

Another reason I wouldn't use one of these multi-dog pile in sessions is that it can, I feel, teach your dog that that is how he can/should react with all other dogs he meets. The owners of the dogs there are clearly saying that's fine, but the owners of dogs you meet just out and about might not think it's such a great idea! I prefer that dogs know that they can say hello quietly, then have a quick run about without it boiling over, but then come back quietly when called. It's not all that easy and requires a bit of work, but that's the ideal for me so worth working towards.