12 month Rottie play mouthing

Hi I have a quick question. Harley has been in OB training. Graduated from 3 courses..But we seem to have an issue with him mouthing my friends and family. He does not even try it with me. Knowing I am boss, but How can I stop him with others. He just gets so excited when other people are around. He does not jump, but he gently puts hands in his mouth. How can I correct him ????
I try and put him in a down stay, but let me tell you, he seems to forget, so I put him back, or make him leave the room.
Is there a correct way to teach him that it is not correct behaviour, just like he knows with me. ???

I'd keep reinforcing the command, until he calms down. Tucker jumps on people when they come in only certain people that he knows he can get away with it. I DON'T allow it, I hold him by the collar in a sit until he calms down, once settled he can go over to these people and sit beside them for attenshion, any acting up, it starts all over again. Becareful dogs can be very tricky, you think they are going to behave and with a flash in their eye they start again. Little buggers.

Yeah hi. First time on here. I have a ten week old shepherd x collie/maremma pup. He is a mouther too but he doesn't know how sharp his teeth are! Anyone have any good tips on how to break him of grabbing my clothing or appendages with his razor teeth??? I've tried the holding his mouth shut and saying no and I've tried the saying ouch in a loud hurt voice and neither of these seemed to have made much of an impact. How long should it take before noticing a small difference?