Insurance companies typically tell you that all licensed drivers in the household have to be rated on the policy. However, there are exceptions to this rule and this situation seems to be one of them. If your son drives a car that is on your ex husband's policy and if the car is titled to your ex husband, there should be a way around having to list him on your policy. Simply have your insurance company list your son as an excluded driver on your policy. By definition, an excluded driver cannot drive any vehicle on your policy. If he does, there is no coverage for any property damage or bodily injury he causes. It is entirely your choice to tell your insurance company to list him as an excluded driver, and there is no law preventing you from doing so. They may require you to submit documentation that he is insured on your ex husband's policy, but this is entirely your choice to exclude him and not have him rated on your policy.