I have been seeing many reports on crop destroyers and animal killers. So I hope this guide helps you guys out!
How to protect your crops:
I think you made an platform to collect the crops,right?

And you made an entrance to it.

The basic way to keep it safe from people who can't /fly or /jump is making an 2 block tall gate to it.

And lock it with a trusted person.

This can protect from people who don't have /fly or /jump. But sadly some people can do it. So you need to protect your crops more.
Basically then just follow TheCarrotThief 's guide.

For carrots, potatoes and wheat you make it 2 block tall

For pumpkins and melons you can basically make it a block tall since you harvest the blocks not the vines.
and nether warts, sugar cane and cocoa beans you don't need to do anything since no one can break them
How to protect your animals:
There are many animal killers, so you need to protect your animals, but its fairly easy

Hope this helped you guys out!
~Enzo

 

Well non-donors can place a block and then quickly jump over the fence before the block disappears. So you should probably make the fence 2 blocks high.

 

Only if /trusted lol

 

No.. He meant, when a block is placed(While untrusted) it causes it to bug for a few seconds, allowing the player to use that as an advantage to hop over the fence.

 

Yeah, MaisaaPG has it correct. The bug allows the block to be placed for about 1 second allowing a player to quickly jump over. Try it on someone's island if you don't believe it.

 

Thanks, nice guide