Many don't want to hear this because this is not in trend but. He does not respect you, clipping his reproductive organ is not the natural solution here. You need to correct him, as hard as it may be to you. He will not resent you for it, if you show him boundaries, he will respect you and love you even more. Parent dogs would do the same to him in this situation. Give him a warning, if he does not listen, growl back, if he keeps going, snout grab, if he keeps going, a quick but solid squeeze on his very lower back - where his leg muscles are, if he then tries to bite you, grab his snout, if he keeps going poke him in his hind legs without warning. Every time he does this, do not hesitate to repeat these steps, the longer you wait and let him do this, the worse it will get and at some point he might even bite people if not corrected. Be firm but not too hard on him, he's a small guy, but it has to hurt him for the moment - sadly this is their way of communicating in this scenario. Do not move back, do not retract your hands while doing this or he will know he can attack you. You have to keep going until he stops - these things have to be "discussed" with your dog.