What steps can be taken to enforce parental rights if one parent is consistently violating divorce decree (re. custody)?

I am asking on behalf of my boyfriend, his daughter is 12 and his ex has repeatedly committed custodial interference based on what is outlined in their divorce decree (this decree was the result of months of heavily funded legal battling on his and his attorney's part). Her violations stem from "minor" (e.g., the decree states she is to have no contact with him other than email, unless it is an emergency regarding their child, and she sends him harassing text messages) to gross and blatant custodial interference and general malfeasance (taking the child out of town when it is not her time, threats, blackmail). The long and short of it is that this woman is irrational and manipulative, when she violates their decree my boyfriend seemingly has no recourse, he tries not to traumatize his daughter despite the fact that his ex has practically dared him to call the police or "try and stop me." It's not as if he wants full custody, but simply that she abide by the decree and respect his parent time with his daughter, stop infringing on his time and violating this decree which was not easily put in place. He has scrupulously documented these incidents and can provide proof of countless violations. How can she be held accountable for this? When these situations arise, his attorney tells him to call the cops, the cops tell him to call his attorney. She is threatening to prevent her daughter from traveling with her dad for Thanksgiving, it is clearly stated in the decree that it is HIS time with her. What can be done if she follows through with her threat? What in your opinion is the best course of action?