If you want to stop griefers, here are some ways:

The trick

Tricking them are hard., but this is a great way!
Put wood pressure plates on the sides of your wood house. Have pistons open a lava pit when they walk in. Place a diamond block in the middle and make it impossible to jump over. This is one of the best ways to stop your average griefer. Mostly because they are young and not very smart.

The spy

Make a grief attraction house, then use an invisibility potion. Watch for a while and advertise your house. When the griefer comes, kill him, and report him. He's done for! If invisibility potions are disabled, choose another way.

Plain report

Go on the website of the server, report the griefer. He's banned!

Troll VS Troll

After your average griefer griefs your house for the day, TPA to him telling him you want to check out his house. Use an invisibility potion, then when he leaves, get out lava buckets and trash his place! Leave without people finding out you did it. He will lose all of his items and might never grief again.

Fix-it

Be prepared! Get as much supplies as possible. When a grief is active, fix everything while he griefs. He will eventually get bored and leave. This might not be a good way, but it may help.

Blow-him-up

When a grief is active, blow him up! Haha. Troll.

_________________________

Well, I hope you like this guide. Please diamond for more!