What do plants have to protect themselves against humans and animals?

The most common would be by thorns on the plant.Some plants have hairs on them that when in contact with skin cause rashs or irritation.(example poison ivy).And some plants emit chemical messages to other insects to protect them such as ants or wasps.An example would on certain plants when a caterpillar feeds on a plant it releases chemicals to attract wasps to that location to attack and maybe eat the caterpillar.