(Tired after day of working 12+ hours, so this might be curt or stupid.)
Now, normally I do try not to discuss plans in ooc when our characters wouldn't be able to (they have to make a snap decision often based on incomplete info, so not discussing it seems less meta-gamey) but for now I'll break that rule due to the... severity of the situation.
Now, I've thought about ways of defeating an arbiter before quite a bit, and 'limiting his mobility', while sounding nice, isn't the best idea right now I think, for the following reason:
The arbiter points one hand in your direction and a set of thin metal cables dart out, flying down toward you. You hop back, out of their way, and they hit and embed themselves in the ground. Everything hangs for a moment before the cables snap taunt and suddenly the arbiter is flying toward you, its club swinging in weird patterns, shockwaves bursting in slow motion around it.
They can use their cables to very quickly zip around. So I don't think pushing him in the air will really work all that much. As for even hitting him with an amp, when renen asked how to defend against amps doc basically said "you can hit them before they finish their thought". And arbiters are just as fast. I doubt one'd even be able to hit a moving/dodging arbiter with any sort of non-AoE, barring exceptionel skills/gear (eg Renen body) or something like it. And I do think he'll be able to spot Lyra, I'd be surprised if it doesn't have something like cameyes-but-better installed. It might even spot the movement of the air molecules when she moves.
This, of course, all assumes it won't be hit by some sort of Worf effect.
((Incidentally, amazing how people say IC they'll follow every order to the letter, yet fail to follow simple instructions at the first real sign of trouble. :v ))