deer spray?

Deer spray is a repellent you spray on plants to keep or deter deer from eating your garden. It is normally a bitter substance, makes the lettuce less appetizing.
Some people use dried blood or pee from a big dog. Normally the deer pick and poke at a garden and leave with a belly full anyway.

Chilli powder also works.

I also use chilli powder when, on a fine summers day, I tend to spread my nuts over the bird table, as it stops the squirrel from having a quick nibble.