Use A NaTe Formation
Wall your Arcane Tower in using Farms in this classic "NaTe Formation" from Warcraft II. If the tower is out in the open it's more easily killed by melee units. The only challenge is repairing it if it's being attacked.

[ Click to Enlarge - 176 KB ] The NaTe Formation used in Warcraft III to protect an Arcane Tower.

Scout Farm
Place farms a ways out from your town. They are only 80/20 and can be used to give you a warning that the enemy is coming your way. When the enemy comes up on your farm, their natural reaction is to attack it. While they are attacking it, you can walk back to your town and defend it. The enemy thinks they are hurting you by killing your farm, but not if it's an extra farm that you're not using. It's hurting the enemy more than it is hurting you by wasting their time and giving you extra time to defend.

[ Click to Enlarge - 142 KB ] Tray places Farms outside his base.