I've heard it was hard but managed to get my ex to agree to it (that's the hard part). I have sole custody and he has visitation (no overnight visits) this was mostly because:
a) they are all young (5, 3, 1)
b) he has prescription drug and health probelms
c) he hasn't really got anywhere to take them as is sharing a flat with a friend.
He signed the consent orders so it's a done thing.. but can be reviewed (at his expense this time) later as the children grow up. I don't have a problem with him having overnight visitation as long as he takes a drug test to be sure it's safe for him to be around the children. But I'm not going to get the consent orders revisited - he'll have to take me to court next time and he can pay (I had to pay $600 to get the consent order put together and he never paid a penny).