I echo the advice above. At 4 months, it doesn't sound like dominance, it sounds like he's playing and he just can't accept that other dogs don't want to romp around just like him! My Ruckus comes on strong with the introductions, barely giving the other dog a chance to say hi before he sticks his face in their crotch (no polite way to put it) so I taught him to wait until I tell him its ok to say hi (this took a year and lots of treats) but I'm still extra vigilant just in case the other dog isn't s bully lover.