My fake/plastic owls are totally ineffective except for short-term use in a very close-proximity area (we do have owls that nest behind our house):
I had a female cardinal who persisted on trying to build a nest on 2nd story steep-sloped bay window roof that was sheltered under our eaves; all her materials consistently just slid off.
After literally 2 weeks of cleaning the nest trash off the deck every day, I hung the owl from the gutter about 6' away - no effect.
I then hung the owl right at the target nesting area. The cardinal would perch about 4 feet away, but become visibly agitated.
She did give up (immediately zero nest trash), and did not return the next year.
Since then I have used the owl effectively two more times for other "target" areas.
BUT, I sat an owl on our deck rail and the squirrels never even seem to notice it one time, just squeezed around it while running the rail.