The most effective method for keeping one's base & defensive fortifications safe from any and all invasion events is to drop everything you are doing and run outside your base beyond your defences. Enemies will almost always engage your character immediately, although because the detection range of trolls is so small, do not run too far away from them. They will head for your base/defences if agro is lost, but usually a well placed arrow shot is enough to gain their attention. I have dug a donut-shaped killing-pit, where I engage invasion enemies. It is simply a circular pit with a raised centre. Find a hill outside your base (but not so far that it is outside the usual red raid event circle on the mini-map) and dig a trench around it leaving the earth in the middle untouched. This will create a raised central area where you can pick off creatures from range, that are in the trench or circling on the outer edge. You may want to flatten the central hill and add some stakewall to stand behind as defence against ranged enemies. I cannot stress how important it is to run out of the base as quickly as you can once the invasion begins, as enemies will attempt to get to your location, destroying anything they can between them and you.

Earthen walls will keep wild animals out. Because they are indestructible they are the best defensive measure in the game, but they can be costly in that it requires a fair amount of stone to construct them. Another cheaper option is to dig a trench on the outside of your walls. Make the trench at least 1.5 times your height and it is advisable to dig it far enough away from your wall that the reach of a troll cannot make contact with it. Surprisingly it does not take a very deep trench to trap even a troll.

wild animals are the least of your troubles after a while.
read the billionty posts on how to keep your base safe from attackers (esp log trolls)
which boils down to one or more of
- deep moat
- private island
- terrain wall (raised terrain ring)
- anti-spawn
- no path to base (similar to moat and terrain, but can exploit natural terrain or other things.

IIRC keeping an animal farm nearby should reduce the amount of wild animals in that area.

Originally posted by calicovi:

is their any way to keep wild animals away? they keep breaking my wall

Build high earthen walls and a trench around. Most creatures in the game are vertically challenged so they'll become a non issue. Also, make sure to set workbenches or similar that prevent reduce spawnage around (or ir) a base to also keep help.

Fires. Torches, sconces , Bonfires all should keep the actual animals and Greys away. Others your mileage may vary