The turn over rate is high. A tower controller is leaving tomorrow. You never know when they will hire. The best thing to do is sign up for email notifications from Flight Global and the SERCO Middle East company site. You can input your CV into their system in advance. This way you will be ready to submit an application when they start hiring.
http://www.serco.com/middleeast/
Search Aviation & Aerospace Jobs on Flightglobal Jobs
Good luck.