I consider myself a pretty good pilot and I have downed a drone due to a phone line close to a roof I neglected to spot on my preflight. A guard would not have helped with my mistake of not carefully checking my flight area that day. My landing and takeoff areas are always out of bounds to anyone but me or my spotters. Cones, Tape, and signs displayed. No one allowed for 40 ft. No exceptions! There really should be no way of hitting anyone or anything while taking off or landing. If you think there is a risk You are flying to close. Now if you do what I did and fly without checking the area carefully enough the guard might help you from getting the gimble ripped off the drone by the wire or branch it tangles with. But as everyone is saying the best guard is to guard against ourselves making mistakes.