* Contracts. Watch this talk by Obie Fernandez[1] and take a look at his Master Services Agreement + Statement of Work bundle (paid for, but totally worth it). Not only does it protect you to some extent legally but you come across as a lot more professional to clients.
* Charge more. I have a comparable amount of experience and I'm charging around double what you've listed on your price card. Many good things fall out of charging more. Even if you don't intend to charge a higher rate, I would at least quote higher on your price card page for more negotiation room.
Good hunting!
[1] http://www.infoq.com/presentations/fernandez-sales-do-the-hu...