Hi im trying to code anticheat in c# for unity games 

But i cant detcted dll injection actually i try loaded dll and moudel but itsnt work becuse its mono inejection

Any buddy can help me?

There is already a few anti cheat plugins for Unity in case you didn't know...

Code Stage - Anti Cheat Toolkit is one I have seen in lots of unity games, its not free but does detect injections

im not access to main source to add codestage toolkit im want to detect by processe do you have any idea for this??

Before you potentially dump $50 on CodeStage, look around for free options. 
Most of what's offered in his library is already free. 

Protected memory/variables:
 - https://docs.microsoft.com/en-us/dotnet/api/system.security.cryptography.protectedmemory
 - https://gamedev.stackexchange.com/a/9851 (Xor'd value, same as how CodeStage protects.)
 - https://www.alanzucconi.com/2015/09/02/a-practical-tutorial-to-hack-and-protect-unity-games/
 - https://github.com/Ymiku/SafeInt
 - https://github.com/pedro15/UniToolKit

Protected player prefs:
 - https://www.alanzucconi.com/2015/09/02/a-practical-tutorial-to-hack-and-protect-unity-games/
 - https://gist.github.com/ftvs/5299600
 - https://github.com/rawandnf/SecurePlayerPrefs
 - Any kind of encryption you prefer works for this.

Generate Code Hashes:
 - Use System.Reflection for this. (MethodBody -> GetILAsByteArray -> hash etc.)

Detect Speed Hack:
 - This is done by monitoring the ticks of an application in a timer/thread checking for any sudden increases that cause the timing of the app/process to be considered fast/slow. 
 - https://github.com/WizardVan/UnityDetector

Detect Wall Hacks:
 - This is done a number of ways depending on what kind of detection you are looking for.

Detect Injections:
 - Walk/monitor the app domains assembly list for unknown modules. (AppDomain.CurrentDomain.GetAssemblies())
 - Track a list of valid/allowed modules + checksum hashes.
 - Track IL edits to functions via hash checks.

Keep in mind all of this is bypassable, editable, etc. by a hack/cheat/mod so while you are adding a layer of security it will only work against certain people whom are not familiar with bypassing this kind of stuff.
 

@kao,  Reversed some really cool "Unity3D protection" checkout his blog. You will get some idea about protection.