Deny the use of Reflection inside dynamically included dll

I'm currently working on a game which has the possibility to create a custom AI which will then get called through reflection. Now I want to deny the use of reflection inside the dll.

for calling methods inside the DLL I'm using this:

Assembly DLL = Assembly.LoadFile(pathToDLL);
type = DLL.GetType("Namespace.Sample");
instance = Activator.CreateInstance(type);
type.InvokeMember("methodName", BindingFlags.InvokeMethod | BindingFlags.Instance | BindingFlags.Public, null, instance, new Object[0]);

Now the problem is that inside the dll, there is the possibility to changes private attributes through reflection. There is only one class inside the dll which need to extend a class in my assembly.

I've already tried to do it with

[ReflectionPermission(SecurityAction.Deny, TypeInformation = true)]

but that do not get inherited.