About to give husband an ultimatum to get help and counselling - could use suggestions and advice from others' experiences

I posted earlier on here about my husband not being interested in parenting tasks.  I've been to a therapist for myself and recently went to one for my 3 year old son.  Both therapists told me that my husband and I need marital counselling at the very least for things to improve, and that he desperately needs individual counselling (of big concern to them both is his impatience, such as not letting the 3 year old use the potty and not sitting through family meals).  My husband has refused to go to marriage counselling when I had brought it up a few times over the past months.  My 3 year old is definitely being affected by the situation now.  I am ready to give my husband an ultimatum - we go for counselling or the kids and I leave...or something like that.  Have any of you done this?  Any suggestions on how to make it effective/non-confrontational?  Thanks in advance for any help!