Lots of walls are huge setup fodder, especially Alomomola! I have a Curse Muk that actually maxed out with 6 Atk and Def boosts against an alomomola and continued to sweep what was left of his team. In terms of actually walling it can go for hours, and Sealeo has taken down Articuno numerous amounts of times (he usually can't hit Articuno super-effectively either, and ice beam is neutral). If thew opponent starts setting up then usually what I do is use ice beam and go for freeze hax (it works sometimes, the opponent generally gets greedy once they see that I'm not switching) or Sealeo dies and I bring in specs Girafarig to finish the job, generally outspeeding the opponent. Also Girafarig has sap sipper, so if I can figure out when Ludico will stop boosting I can switch to Girafarig to absorb the giga drain and then let hydro miss miss.
With right support Sealeo is beastly (as beastly as a wall can be), and it holds the honour of being a great wall, neither physical nor special, just making it a great defense on your team. Every team needs a good wall, and even though Sealeo doesn't have leftovers, he is almost never 3HKO'd so he can generally attack with the sleep talks, attack with an attack that he knows (ice beam or surf) and then rest again. Not to say I haven't tried out Walrein, Sealeo worked better on my team for me.