Pete if your worried about things like that I would have a lawyer write up something as that is what will determine it, not the web host or the web register company.

You can form a company that owns the domain name and assign and even amount of shares to your partner and yourself.

Each person can sell their shares to the other for a later agreed amount should it come to that.

I don't know where you live but if it's the USA, you can use a service like Legal Zoom and set up an LLC or S corp and divide the shares between you and your partner however you'd like. You can use a lawyer but if the deal isn't complicated, you can do it yourself.

You could have this LLC own just the domain name. This will protect you both.

Agreed - form a company and the company own the domain name.