I have a Scarecrow motion detector sprinkler, and it is excellent for short-season fruit like my lychees in the front yard. It keeps the birds and squirrels at bay just barely long enough for the fruit to ripen and me to actually get some of it. It works at night as well, because in summer when the lychees are ripening, we have fruit rats, too. I can't use it in the back yard - if I do the cat comes in wet and very miffed. It's also too leafy in the back yard, and the leaves moving in the wind sets off the motion detector too often.
Luckily we also have many owls, and lots of hawks, but I don't like letting the resident red-tail hawk prey on my songbirds, so he hunts in the front yard, and I 'discourage' him with the pellet gun if he lurks in the back yard. The birdies also have good cover from big birds in my stand of bamboo about 10ft from the feeders.
You're right, Ken, I think a hula hoop would make an excellent catch net. That's truly been the best squirrel deterrent, because they always have a little seed to feed on, and I even sometimes put a scoop or two in the net for them, just because it keeps them from raiding the feeders.
