People
Cats use my shrubbery bed, which is right against the side of my house, for a toilet. I can't open any windows on that side of my house because of the stench. I've tried moth balls, coffee grounds and I've even peed in a coffee can and dumped it in the bed trying to get rid of them, to no avail.
Over the past two years that would be an infestation of English blackbirds. They dig up everything and scatter the soil and ground cover.
Mind you, they've got one good attribute -- they've taken the heat off me. Mrs Didge is a very creative gardener and my "weed it, water it, cut it, leave it" method is so much at variance with her own painstaking care that until the blackbirds arrived, she always claimed that I was the worst pest in the garden.
Oh cats, definitely......cats be gone outta the garden!

Slugs first, they ate my Foxgloves at the beginning of the year, thankfully I managed to save them. Next cats, I don't hate them, but as a keen gardener, cat faeces is not something I want to be sticking my hands in. Cut down Bamboo sticks seem to have worked for me, I don't leave any spaces, I have quite a few low growing roses as well.
This year was stink bugs eating my tomatoes. I didn't even know that was possible until this year.
Slugs that bring the moles that tear up the yard.