Sounds like he needs some basic obedience training 
When he starts to get onto the other dog stand over him and kind of stiffen up and make your voice very low and tell him "Thats enough!" and nudge him with your knee/leg and when/if he looks at you praise him and get him to walk away from the other dog with you. If he keeps at it and do an "AH AH" at him and then "Thats enough!" and a bump, then have him walk away. If he keeps at it do the "AH AH" and then grab him by the cheek (gently) and look him dead in the eye and give the low "Thats Enough" and lead him away by the collar. After you lead him away give him something to play with like a toy or a ball.
Good luck!
When he starts to get onto the other dog stand over him and kind of stiffen up and make your voice very low and tell him "Thats enough!" and nudge him with your knee/leg and when/if he looks at you praise him and get him to walk away from the other dog with you. If he keeps at it and do an "AH AH" at him and then "Thats enough!" and a bump, then have him walk away. If he keeps at it do the "AH AH" and then grab him by the cheek (gently) and look him dead in the eye and give the low "Thats Enough" and lead him away by the collar. After you lead him away give him something to play with like a toy or a ball.
Good luck!