Might be useful to think of these boundaries as being for you. And also, consider how we deal with other people trampling them.
For example:
Say a woodcutter comes onto my land and starts chopping down my trees...I might say 'hey! Stop that! Well...actually, there are some loose logs around, you can gather them.
The woodcutter pretends to agree. But the next day you come back and see he is chopping down trees again.
I say 'hey, that's not ok! Well, I suppose there are some half dead trees you can remove. They aren't very sightly anyway!'
The woodcutter pretends to agree. But low and behold, the next day there he is back again. And - He's chopped down every fucking tree on your land.
What you should have done, is on day one, told the cheeky bastard to get tf off your land! And when you got home that night, made a mental note to yourself to call the police if you ever saw him near it again.
Because woodcutters chop wood, it's in their nature. Set the boundaries for yourself so that you don't take any shit. The second you see them for what they are, enforce your boundary ON yourself. Don't play nice, don't compromise, don't think about what that cheeky git wants. Just act to protect yourself. Enforce your own boundary.
Which generally, should be to remove this person from your life as fast as possible.
Setting boundaries for shitty people, hoping it'll make them less shitty, is relatively pointless. Better to set them for ourselves regarding non negotiable in what we tolerate. If someone breaks a non negotiable, we remove them from out life. No compromise. No more second chances.