I have two children ( 7 and 4 y/o) with my ex .
We have been split coming up to 4 years.
He has saw our daughters when it suits him. He has gone months without seeing them or even asking how they are. Even times where i have had them ready and waiting and he hasnt showed up. I could go on and on.. But getting to the now.. He hasn't saw them for coming up to 6 months now.. He has told me he will see them soon.. But i dont want my children messed around and asking where 'daddy is' when he vanishes off the face of the earth again. 
He is a vile person. He has no respect . i dont feel like my children are safe and looked after when they are with him .
Theyve came home in the past unwashed and hairs not brushed. My eldest told me he let my youngest up and down the stairs alone ( she isnt used to stairs as i live in a flat) ...
he has been violent to his current partner ( bit her face - he admitted to it)
I want the best for my children . and he isnt what a dad should be..
Ive told him all of this but he doesn't seem to care. He says i cant stop him seeing them but im at the end of my tether ive gave him enough chances to prove himself and he isn't. What can i do 