[ffcmike]

You can always check to see if certain important values are changing unexpectedly in the middle of a process.
For instance within a movement system you can store the X/Y amount that is intended for the player to move, set the new player X and Y, but if they were to have moved a certain amount more (there does seem to be false alarms when checking > value exactly, so I check just a slight amount greater) before that script has even finished running then it has most likely been modified.

This method seems to be very reliable at catching a particular fairly widespread trainer,
but ofcourse this doesn't help much for stuff like modifying computer speed or framerate.

There are also instances where you can tell if someone is memory editting a function where a check that should always return true with the given parameters turns out to return false.