If it is only certain genres of porn that upset you, make sure to talk about this with him and let him know why it makes you feel the ways you do.
If you feel okay with the porn, the concept of keeping him from watching it should not arise. This behavior causes distrust in the relationship, and can cause him to keep his porn use hidden from you, or cause tension and discomfort while talking about the subject. Unfortunately, if you know you are not okay with porn and you try to keep your significant other from watching it, you may fall into a pattern of being the 'porn police'. Don't try to ban it, but establish each other's boundaries to the relationship.
