Use the following trick to prevent your useless wingman from stealing your kills, especially in the arena mode. The key is his or her weapons selection. Instead of giving them medium to long range missiles like Sparrows and AMRAMs, outfit them with just short range missiles like Sidewinders. By doing this, the wing-man can help defend you if someone gets on your tail, but will not be able to steal a kill if your missile misses a target or just wounds it. In Arena mode, also outfit the wing-man with an anti-ship missile. There are Bosses that are ships that require several Harpoons to sink. If you run out of missiles, switch the wing-man to ground attack to take out the ship.