Sorry if this isn't posted in the right place.
DP has the most hideous relationship with his ex. Long story I won't bore you with.
This year was the culmination of a court battle over spousal support and he won. The consent order has been granted by the court, he's paid the financial settlement, job done.
He saw his DD on Sunday and Ex was, as usual, horrible to him.
DP is about to move in (I didn't figure anywhere in their marriage breakdown which happened 6 years ago) and we need to tell Ex about it.
Problem is, she's sworn blue and blind that if he does move in, she'll come after me for half my house as 'if she can support you I should be getting the money you're saving' 
Is there anything I can do, any document we can have drawn up, any legal protection against this? I'm not worried about him at all, he's welcome to all I have (within reason - he's not having the cat!), but as long as the moneygrabbingluncatic ex is around I need to protect myself. DP agrees we should do something but we're not sure what.
Any ideas? Oh, and we're not helped by the fact that my mother has heard of someone in a similar situation 'you know, Margery, Margery from the golf club, well her daughter's best friend's auntie's third cousin had to sell her house...'