Step 1 You need to make your base big so if your standing in the middle of it, your friends can't hit you. Then, make sure that every single block around your base is at least 3 blocks tall
Step 1: Step 2
Then you must put a slab of any type down 1 block away from your base
Step 2: Step 3
Then, you can try to get on top to our base, and try to kill your friends when they TRY to get on... And you can make your base bigger and your done!