Firstly you have to make sure your whois info is as detailed and accurate as possible. If someone will ever want your domain, this is the main thing he can count on. This is a great way to verify if your domain still has your contact data, and didn't get modified in the meantime.

Secondly, when you buy a domain write down on a piece of paper your business plan and the business area it targets and stick it to the act that proves the domain is yours, the go to a public service to legalize the papers. Then, you will have to try and register the domain under your trademark in the country you live in. This is especially good is your domain gets stolen by someone because this way you have legal rights over that name and you can get it back. When you start you business with that domain, make it public as much as possible with the TM sign next to it. Place it over the web, on banners and business cards, commercials and so on.

In case you get various demands and offers from firm or persons to buy your domain, it is better not to give them an answer before consulting an attorney. If you answer them, then they can make use of your info when trying to steal your domain. If you are interested to sell and you get a good offer, prior to giving out technical information like passwords, check out the buyer's background and credibility.

If you happen to receive a complaint from the court responsible for domain names, make sure you respond promptly or you have all chances in the world to loose your domain without the possibility of getting it back. You might want to hire an attorney if your domain is big and you really need it for your business's well being. Also, do not put malicious links on your website or links to adult sites. In case of a trial, the person that wants your domain name will use them as a weapon to try and destroy your credibility.