Need of repeated approval if Physical custody of child is been granted

Hi, I am in midst of discussion for an amicable seperation, wherein my ex-partner is giving the custody of my son to me on the ground that she is not in a capacity to manage his agressive behavior, I am an IT professional, currently outside the country on a long time project and intent to have my son with me and bring him up as a single parent, Given the nature of my job, I might be required to move countries (subjective), wherein i am asking for a clause that, in future my ex-partner will not object of my son residing with me incase my current location changes. In the past, my ex partner has on whims barred access of my son to me and my family, wherein they have been situation that even if I have to take him for an holiday, I had been told that if I didnt provide information of who all are the people going to be traveling , she will not allow him to travel. Thus want to know if I have to take approval each time , my project location changes and I want my son to be with me. Regards Dan