Can you practice airsoft in backyard.

I want to know if I can practice airsoft (It is not metal palette it just 6mm plastic rounds) in my backyard with neighbor leaning on the other side of the fence. I am leaving within the city, I have read that for airsoft gun within the city, if you have a certain amount of area I can practice airsoft. Do I need to notify my neighbors about it when I am practicing. Is there anything I need to do like setup vise.