cohabiting couples property rights

if a person owns a property and decides to allow another person to live with them on a cohabiting basis...if this is the right expression?..not as a person under say rent a roomscheme what right could the non owning person claim in event of a break up?. Or put another way what steps could the property owner take to ensure no such claim could arise. I appreciate if the non owner was making financial contributions which had the effect of financially benefitting the owner then a possible claim could arise.

It can get messy. The way to avoid this issue is very unromantic (on purpose, because as Joan said they don't want it too easy to live together) and involves getting legal advice and signing a declaration.

Here's a starting point:
http://www.citizensinformation.ie/en/birth_family_relationships/cohabiting_couples/

The Law Society has published a precedent co-habitation agreement which is a starting point for this situation.

Check out the Civil Partnership and Certain Rights and Obligations of Cohabitants Act 2010 for more info - here.