Concerned

It's one of those mornings when I woke up way too early and worries have been gnawing at the edges of my brain. Today I'm mostly bothered by Kyo's biting problem. I've talked about this before, but the issue was brought back up this past week when he bit Jetta while trying to play with her at the park on Wednesday.
As I mentioned before, Kyo is staying with my parents while Glacier and I are in Michigan. My mom is doing a really great job of making sure Kyo gets the proper amount of exercise and stimulation and he seems to really like her. Just the other day, she was lying on the couch and he climbed up beside her and laid his head in her lap. He's a great snuggler! That said, in his excitement and puppy playfulness, he bit Jetta on the back of the leg at the dog park and made her yelp. This concerns me for the obvious reasons-like how he should not be hurting dogs-but it also may mean that I'll have to give him up. I really don't want to, but I can't figure out how to get him to stop. It seems that after he gets comfortable with a dog, he is likely to bite them while trying to play with them. My mom says it looks like puppy play, but because he is so big, he accidentally hurts the other dog. Again, he's not biting other people's dogs: just the dogs he knows like Jetta and Glacier. He doesn't bite roscoe, but I think it's because Roscoe tells him "no" just by looking at him. If humans nd dogs alike draw boundaries for him, he seems to respect them. My other parents' dog Flash, is a bit grumpy and doesn't like other dogs in her space and all she had to do was growl at him once and he leaves her alone. When I've been doing obedience with him, he picks it up quickly and is eager to learn. He has separation anxiety (as many Great Danes do) and this makes him a people pleaser.
Part of me doesn't wonder if the biting is out of anxiety. I got him in March and things weren't quite stable. Mr. K would be visiting us for a couple of weeks and then he would be gone again for another couple of weeks. Now, Kyo is at my parents' house in a strange city with two new dogs, which isn't exactly stable either. I'm hoping with more consistent living conditions and more obedience training this biting problem will stop. If not, I will have to find a new home for Kyo and that pains me grately. Everything I've read about dog misbehaviour always makes comments about dog owners giving up on dogs when their problems can be fixed. They talk about how dogs end up in shelters all of the time because they are not given what they need to thrive. I don't want to be one of those people-but when is enough enough? Why can't I seem to get any help for this behaviour? I can't seem to find any literature that addresses this particular problem. When I talked to the dog trainer about it, she didn't really know and just suggested that I distract him with something else like a toy. She didn't really explain how to perform this or the logic behind it. I thought that if I gave him a toy while he's biting Glacier then I am rewarding him for biting? I'm at a loss. I've thought about getting another dog trainer when I'm back at home to see if they can help me solve Kyo's biting problem. If anyone out there has any ideas, please send them my way. My heart breaks to think that he may seriously injure a dog and/or I'll have to find him a new home. He's already been through the surrender/adoption process I really don't want to do that to him again. :( I just feel like I am/have failed him somehow.