Trouble in PvZ land

I'm having trouble with mutalisk harassment in PvZ lately. I,m trying to control the muta flock with canon coverage and psy-storm.. it work some time, but i felt like the mutalisk flock have ton's of map control.. which mean that the zerg can expand as much as they want.. i cannot drop because the mutalisk can catch it.. some people suggested that i use blink stalker. I will train more for the time being =D Hopefully i can find the answer.