Alliances are usually responsible for the conduct of their members

One thing you can do is to try to talk to the player that is attacking you. Call them to stop attacking you,  Little Empire Mojo because you're just like everyone else who wants to play the game and not get bullied.

Ask politely, without threatening.  Buy Little Empire Mojo If you make empty threats, they may be recognized and probably result in further attacks.
If the attacker is a member of an honorable alliance, speak with the chancellor of that alliance. Alliances are usually responsible for the conduct of their members. Again, be polite.

If they are from a dishonorable alliance or are persistently farming you and won't stop,  Cheap Little Empire Mojo then the are a few things to do to annoy them greatly and should stop them:

Hide your troops in sanctuary - in the castle
Keep resource levels below storehouse levels. A level 10 storehouse with level 10 shrinking powder keeps 2 million of each resource safe, excluding gold. Cheap Little Empire Mojo

It works like a Katamari game: the more clay you take on

Playing as a blue rolling clay pebble, you poke, prod, and sweep your finger to gouge a path across the clay landscape. As you go you'll squish a whole variety of clay monsters, Little Empire Mojo  making yourself bigger and faster as you go.

Using the clay you've acquired you can buy more monsters and increase the size of the level until you restore it to its full glory.

It works like a Katamari game: the more clay you take on, the bigger monsters and objects you can absorb.  Buy Little Empire Mojo However, you'll want to avoid those that are too big, Cheap Little Empire Mojo  as you'll lose clay each time you hit them.