Mortars, Wizard Towers, those AoE/Splash damage defences are a pain at times with Wall Breaker use. Just deploy a bit off to one side of the decoy units if able.
Had more than a few humours, but frustrating, times where I time things perfectly wrong, and have a wall breaker run up to a wall, only for a long shot mortar shell to hit where the little bone head stopped at... several times in a row.
*deploy WB*
*watch*
*Mortar Shell hits right as WB stops at wall*
*deploy WB again*
*watch*
*Exact same effect with Mortar!*
*Deploy 3rd WB*
*watch*
*Mortar Shell for the denial!*
*waits...*
*Deploys 4th WB*
*See Mortar shell hit ground before WB gets to spot*
*Watch WB run up and do it's job!*
*yell "Finally!" and keep attacking*
...
...
*Only get 1 star from wasting so much time and wall breakers on silly perfectly timed mortar! Duh!*
*Cure at Murphy's Law again*

