Colleague hijacks my work + possible redundancy

Hi MT-managers.

A collegae (“J”) regularly interferes, or hijacks my work. I fear myself becoming redundant.

My environment;
* Employed for 1 year with temp contract (expires Nov-2012).
* Global multinational, non management function.
* First time in this role as Operations Process Coordinator. Non management.
* Three colleages for various backend systems.
* all tech work offshored to E-Europe, India (EndUser → myself → offshored workerbees).

Background;
Management instated that systems has primary responsible, and a  ‘backup’ coordinator so to guarantee critical processes are cared for incase of sickness/vacations. All four of us started the new job on the same day. “J” as my ‘backup his own systems are often lacks enough ‘tickets’ to solve. My other 2 colleagues has distinct, different process to care for which requires thorough XML experience of which J has none. He would covertly talks to users drawing attention to himself.  Yes, i feel threatened.

Health;
F has health problems and often is on sick leave (already 4 times this year) for at least 7 days or more. unlike him I don't interfere in his job as a few times i did he lost his cool, and i withdrew. Cruely, his health problems could work to my advantage as often his processes are left stale in his sick leave.
Socially F is an analyst who cannot take a joke. He unsuccessfully tries to chum-up with our manager. F is good at his job (or pretends to be). We sit directly in across from eachother.

Resolve;
F and me has ‘talked’ to each other about his hijacking of my work. For now its a draw.

1-on-1;
I’ve mentioned it to my manager in a weekly 1-on-1. Rightfully his concerns was guaranteeing the process, and he felt the ‘team’ tension already.
Overall my performance is good. Not a star performer (not yet!). My manger knows about my desire for staying in the Group, even if its in another ‘market’ (China, Australia, South Africa etc).

To F this is just a job. I am a user & fan of their products and feel ‘at home’.

Remarks
1. Our manager stated that he’d like me to be backup to F’ processes.
2. Both F’ contract and myself expires very soon.
3. Our manager is aware of me and F’ relationship.

Questions / remarks;
1. How can i best stop the interference in my activities?
2. If YOU are my manager, and you know about above situation THEN....
3. Extend (my) contract, or not..?

Any advice, comments appreciated