Well it's gonna be hard to get Umbreon in Emerald, so that's off the list
Instead I would use Skarmory. His great Defense and decent health allows him to be great wall. He walls most of the elite 4, Sydney, Phoebe, and part of Drake. He also completely walls Norman, so if he has always been hard to beat for you, just use Skarmory. The moves on him would be Fly, Steel Wing, Spikes, and any other move you want.
Hope I helped!