Ponerle a algo - Using the Verb Poner in Interesting Ways

You can use the verb poner to indicate that an object, and not a person, is a recipient of an action.

Look at this example. We have a person as the recipient of an action:

Ella se puso un vestido rojo. She put on (herself) a red dress.

In this example, the recipient of the red dress is a woman. Notice these sentences, though:

Les pusieron una cerca a los perros. They put up a fence around the dogs.
¿Le pones azúcar al café? Do you put sugar in your coffee?
Tengo que ponerle seguridad a mi correo electrónico. I have to put security on my email account.

Notice that in all cases, the object is being indirectly referred to. Thus, we use the indirect object pronoun in the third person form.