Moving Luna around is your best bet to deal with a Dredge. as for directly combatting him, your ult can save you from his ult if you have no way to leave it's AoE
With the 'BOOBY TRAP' talent, keep your mine activated near you, if Andro (or any other enemy) comes from behind you, it will do initial damage, alert you, and a little knockback making him lose some precision.