If you already own the assets the cheapest way would be to do a pre nup.  Most lawyers can do this for yourself and your partner, otherwise you can buy some forms off the internet and do it yourself.  Laws in each state vary, I think from memory here in WA once a couple have lived to together for 2 years then there assets are dealt with as 1 (unless pre nup is in place) before the 2 year mark for couples living together then its viewed at who owns the asset. This is then different again is the couple is married.