I'm afraid you need a GOOD lawyer, because you have to sue your client -- which will cost you even more money, with the risk of not getting anything back.
I usually follow an advice that was given to me when I was still a teenager: Always demand an advance of 1/3 of the estimated bill BEFORE you begin to work. Then demand another 1/3 when you are ready to ship/roll out/deliver. That leaves only 1/3 open after the customer has received your end of the deal. If he does not pay then (and we all know how lousy payment morale is), it won't hurt you that much.
I usually follow an advice that was given to me when I was still a teenager: Always demand an advance of 1/3 of the estimated bill BEFORE you begin to work. Then demand another 1/3 when you are ready to ship/roll out/deliver. That leaves only 1/3 open after the customer has received your end of the deal. If he does not pay then (and we all know how lousy payment morale is), it won't hurt you that much.