I have the usual 'legalese' written into my contract re: non-payment, interest, small claims court, etc. However, this has never been an issue for me because I require an up-front deposit before beginning work. If a potential client isn't willing to pay a deposit, I don't wish to work with them, anyway! Those who HAVE made the deposit in advance have ALWAYS paid their bills on time without any fuss. And, as their bookkeeper, I know what state their finances are in and whether they are likely to miss payments, in which case I institute a pre-pay policy with them after the initial month (which I notify them of right away, of course).