Trust me, there are ways of stopping them in their tracks that have nothing to do with hurting them.

[Lyle pulls a sniper rifle out of the bag and crouches with it near the roof's edge. He takes aim and pulls the trigger.

A beam of solar energy fires from the barrel of the rifle. It hits a pillar near where the Grimer are, blowing a hole in it and toppling it in the Pokémon's path. The road is now blocked.]

There we go! That buys us some time.