Relocation: Mother Wants to Take Child Out of State

My question involves a child custody case from the State of: California
My friends ex wants to take their 2 year old child to live in Texas where her husband is stationed. What can he do to keep his daughter here? She has most of physical and legal custody they do have an agreement where he gets her the first and last week of the month. And have to get permission from the other parent if they want to take her out of town. Although he luckily gets to have her if she needs a sitter or just needs a break, he's even picked up and watched her son many times. When they first went to court she told lies about him and his family saying they were drug addicts and drank all day long which is the furthest from the truth. They did make him take a drug test which he did and passed. When they went to court he didn't really speak up because he was felt he would get too emotional and i think he was intimidated because she had an attorney. She's made reports that he's hit her, he's violent and many other lies...She has actually given him a black eye and slapped him in front of his brother and friends before. She even asked that his sisters not be able to take him to drop off or pick up the baby from her house because they were "violent". She did get into an altercation with one of his sisters because she was in their mothers face talking very ugly to her about how she didn't shop at place like walmart petty things. The agreement said they should have no contact unless it was about their daughter she violated it to ask him if he had a gf and many other things that had nothing to do with the baby he never reported it because she would threatened him saying she would go back to court and take their daughter. He's always been somewhat afraid of her because he knows her family hates him and she does have the money. She's gonna claim it's best for her daughter to be with her and her husband and that he doesn't have a job and lives with his mother. Although she's cheated many times on her husband while being here in california. He does pay child support too.f Despite him being unemployed his daughter has never gone without always clean and happy. His family is very united always does family get togethers and just has a good time. He's gotten rides from me before to take his daughter to the park or doctors appointments. He has such a good relationship with his daughter he's such a good dad. Even his family gets so excited when he gets to have her for a few days they all rush to be with her and spoil her. She is now taking him back to court in a month to try to take her and saying she will let her come on holidays. When he got served he set up an orientation for a medical school and is desperately looking for work. We know she's gonna do all she can to make him look bad in court. Not because he's my friend or anything but i've witnessed how cruel she can be she starts most of the arguments talks down about him to almost anybody that will listen but he never can prove the type of person she is. There is no doubt she loves her daughter but she's doing this out of spite because he's moved on and no longer fears her or listens to everything she says. What can he do to keep his daughter in California? Anything he can say or file that will prove he can care for her just as well as her mother?