Ask HN: Should/how can I open source my new SaaS project?

I've had an idea for a new SaaS project which I'd like to open source if possible, but I don't want anyone simply duplicating my work and undercutting my pricing! (though I'd have no problem if people wanted to self host it for their own use).<p>Does anyone have any tips for to how I can achieve this, or any pitfalls that I can expect to come across if I try and open source it? I'm really hoping that someone'll say that there is a licence that'll give me the protection that I'm hoping for while also freeing me to release my code to the public. The GPL licence looks like it _could_ be what I'm after, but I could do with some advice!