You can either go for Ruskol's 4 tiles square or go for this setup and abuse the lawn mower, I prefer the latter since my whacking speed is slower than him, though it's hard to pull off. Keep in mind that if you go for the 4 tiles square you will need to deal with the RNG of buckethead spawn in the final wave, either way the RNG of dropping item (coins, suns, etc) which prevents you from hitting the zombies in the final wave can also ruin everything.