To avoid the cheapness of handing off the planet within a legion so that the 'Contested' debuff never accrues, why not have the debuff be based on the controlling *legion,* rather than the controlling player? Although this would still allow for passing it between sister legions, it would not make it possible to hand it off within one's own legion and keep it constantly at full defense.

Handing it off between sister legions could be made more difficult as well if it took a while for the legion debuff to fade. For example, the Dysonians take Exotica. The Dysonians build up a Contested debuff that gets applied to Exotica. If they lose the planet, it takes four/eight hours for their debuff to reset to 0. This means if they immediately took it back, the debuff is still on.
A legion trade-off would thus mean that the dummy legion would have to hold it for eight hours before the main controllers took it back, increasing the chance that someone else might take it.

+1 good idea.

What if the person leaves the legion? Do they keep the legion debuff timer?

yea I had the same thought Bluecifer this would be easy to skirt unless you have it a person and a legion so if one changes and not the other it keeps going up and when out of legion your old legion still counts to it but that can still be gotten around join another legion instead of just leaving yours. If you understand what I mean.