i want to ban my ex husband from travelling with...

We would like to inform you that if your son is in custody of his father, he may travel with him only with your written consent.
The Personal Status Law prohibits the travelling of the son with the custodian or non-custodian except with the written consent of the other party. Thus, your son will be automatically prevented from traveling unless he has obtained your consent to travel.
The UAE Personal Status Law stipulates that:
Article (149)
The fosterer may not travel with the fostered child outside the State except with the written approval of his tutor. Should the tutor refuse to give his consent, the matter shall be submitted to the judge.
Article (151)
1. Should the fosterer be other than the mother, she may not travel with the child without a written authorisation from his tutor.
2. The tutor, whoever he is, or another person, may not travel with the child during fosterage without a written authorisation of the fosterer.
3. The fosterage of the repudiated mother may not be forfeited just because the father moved to a city other than that in which the fosterer resides, unless the move is for the purpose of settling, is not prejudicial to the mother and the distance between the two cities does not allow the mother to see the fostered child and return the same day by the usual transportation means.