ignore touch on right side of ipad screen

In my infinite wisdom-- this being my first iphone game and a novice programmer to boot, I put a great deal of effort into creating an OnGUI control scheme that is used to control 3D objects. This makes use of horizontal and vertical sliders. Imagine horizontal slider on the left side and a vertical on the right. Control along the horizontal slider and the vertical at the same time are impossible on Apple touch devices utilizing OnGUI without a workaround.

Of course this is because (as I've discovered somewhat late) OnGUI is only single touch (and a memory hog), so my solution is to shift all the controls to the left side forcing the player to use their thumb to control the sliders and GUI buttons and disable touch along the right side(and ignore memory issues as FPS is ok). This control scheme works in this game. Without it, when the player touches the right side to simply support the device while playing, the horizontal slider will either move or funky touch focus issues happen.

I need help ignoring the right side landscape left of the screen for touches. Code would be useful as I'm a novice.

//If touch position position greater than 1/2 landscape left screen width (perhaps as //defined by a specific Rect?...or >=position.x?...or Screen.width/2 ?) don't register it. 

Use raycasting by creating custom layers, and separate your GUI elements from your gameobject and put them into separate layers.

Check this out:

This guy creates a layermask to ignore 2 layers, in your case create one only to accept raycast hits from one layer.

Source code can be found here:

http://www.revelopment.co.uk/tutorials/unitytutorials/73-howtorotateanobjectbytouch