I've gotten a couple of comments about what to do when your dog's play style is so rough it's not a lot of fun for the human end of the partnership and cookies seem like a much safer reward. I probably don't have anything new to say about it, but I'll throw my two cents' worth in cuz I know where you're coming from and I usually have a few bruises to prove it.
Phoenix was pretty hard on my skin until I learned how to play with him in a way that wouldn't leave me headed for the first aid kit at the end of the session. I'll be honest, we still have our share of OUCHHOLYSH*TTHATHURT episodes but they are becoming fewer and fewer. He is a very physical dog and I will accept that playing with him isn't going to be like playing with a maltese. Yeah, there are going to be some bumps and scrapes along the way and that's just the way it is, especially since I have chosen to engage him physically. If he were ever gentle or dainty in his play style, I'd probably rush him to the vet!
One important thing for me was realizing that a dangling toy, held with only one hand, was simply an invitation to "climb" the toy with his teeth. What was at the end of the toy? My hand. So doing chase recalls with a toy flopping at my side was pretty much an invitation to bloodshed.
Probably the best thing I ever learned about playing with him was to give him a specific target to bite. That took a lot of guesswork out of the equation on his part and took the focus off my sleeves or pants legs as potential targets. I use a lot of Schutzhund-type, working dog tugs as toys, along with the occasional plush, squeakie thing or a ball on a rope, but no matter what type of toy I'm using, I make it a point to hold it with both hands and present a very clear YOU BITE HERE surface. I've never done any formal bitework with him but it is very clear he enjoys chomping things as a reward - I just need to control WHERE he chomps.
He rarely misses. If he does make contact with my fingers, it's usually because I moved the tug at the last minute, after he'd already launched and couldn't correct his course, or because I wasn't holding it "properly" in the first place. If I have my fingers splayed all over the thing, I'm just asking to get chomped.
Another thing is to watch the dog's arousal level. Probably the first piece of advice I would have for someone whose dog bites out of arousal (and I am NOT an expert on this in any way) is "Don't practice bad behavior." If he gets mouthier as he gets higher and higher, stop working before he goes over the top. Let him have a time out to regroup and drop below redline. Another idea is to scream YEOUCHTHATHURTOMGIMDYING and refuse to play for a few minutes while the dog considers the fact that he might have just killed his play partner and that pretty much ended the fun. If the dog finds the behavior rewarding and/or is allowed to repeat it, he's going to keep repeating it.
I know when play hurts, it's really tempting to slide back into using cookies-only rewards. But safe and happy play that can be enjoyed by both partners is a powerful thing and worth building, even if you can only play for brief periods before the dog escalates over the top. It's about trust and respect on both sides, even though that's obviously easier said than done when you're dealing with a big, physical, high-drive type of dog. It's up to the handler to establish boundaries of what is acceptable and what isn't.