normal business insurance usually includes EO insurance (errors and ommissions) which should cover you for most things.
doesnt hurt to also put in a clause in your contracts that the client is fully liable for any product as a result of your work, and a legal professional should be consulted.
Im not a lawyer, so do your homework, my reply is just based on my own experience.
**I am not liable for any results based on the contents of this post, and a legal professional should be consulted. 
R