Ztest shader issues

Hi guys, I'm currently using a Ztest toon shader written by someone else to allow for my characters to be seen when behind walls, however there is currently an issue with it, in that the shader is actually causing geometry on the character to draw in the colour through parts of the geometry blocking it, is there any way to have the shader not apply the rendering prioritisation to parts of the model's own geometry?

Here is the shader, again, this isn't mine.

 Shader "Custom/ToonZtest" {

 Properties 
 {
     _Color ("Main Color", Color) = (0.5,0.5,0.5,1)
     _Color2 ("Obscuring Color", Color) = (0.5,0.5,0.5,1)
     _OutlineColor ("Outline Color", Color) = (0,0,0,1)
     _Outline ("Outline width", Range (.002, 0.03)) = .005
     _MainTex ("Base (RGB)", 2D) = "white" {}
     _Ramp ("Toon Ramp (RGB)", 2D) = "gray" {} 
 }

 SubShader 
 {
     Tags { "RenderType"="Opaque" }
     UsePass "Toon/Lighted/FORWARD"
     UsePass "Toon/Basic Outline/OUTLINE"
     Pass 
     {
         Tags {"Queue" = "Geometry+1"}

         ZTest Greater
         Cull Back
         Color [_Color2]
     }
 } 
 Fallback "Toon/Lighted"

}