TARO 3 YEN, HEYDN -

Using PET plastic drink bottles filled with water to scare away cats, that WORKS. At least everyone tells me it does.

It seems best to use not the ordinary ones but the ones that hold like a quart and are oblong in cross-section. The angles catch the sun and scare the cats away it seems.

There is one really, really big problem with this though. THEY CAN START FIRES! I shit you not. Fires have been started by the lensing effect in bright sun so you don't want to have the focus on anything that can burn.

A similar problem MIGHT exist for those hanging plastic bags, so watch out!

Operation Debris Denial (ODD)

Space War Orbital Rapid Denial (SWORD)

High Altitude Denial Eclipse Shot (HADES)

Orbit Denial In OUter Space (ODIOUS)

Operation High GrOund Denial (OHGOD)

DEbris Limit Eclipse TEst (DELETE)

PAcific Night Test In Eclipse Shadow (PANTIES)

High Altitude Capture Kessler Syndrome Acceleration Test 2008 (HACKSAT)

BAllistic Space Test And Responsibility Denial Simulation (BASTARDS)

I had these (well snake fireworks) when I was a kid, maybe 30 years ago. They were black carbony cylinders 1cm long. One thing to watch out for, it will leave an indelible mark on concrete.