When I was in Baqubah, incoming in Baqubah was a daily thing. Sometimes we would even hear them coming in and at other times we would not know about it until the ground shook from the impact.
Of course, in each instance, there was no time to find a secure place to hide. In the beginning we only had one bunker we could run to but they got more and more bunkers built.
Over time the attacks stopped and incoming was a rare occurence. When military units were rotating out was the most dangerous time while the new units got up to speed on protecting the base.