Blending / Lerping between textures in a Unity CG Shader

I can lerp between Colors just fine, but lerping between textures just doesnt seem to work?
What am I doing wrong?

 Shader "Custom/Terrain1"
    {
        Properties
        {
            _RockInnerShallow ("Rock Inner Shallow", 2D) = "white" {}
            _RockInnerDeep ("Rock Inner Deep", 2D) = "white" {}
            _RockLight ("Rock Light", Color) = (1,1,1,1)
            _RockDark ("Rock Dark", Color) = (1,1,1,1)
            _GrassLight ("Grass Light", 2D) = "white" {}
            _GrassDark ("Grass Dark", 2D) = "white" {}
    

        _Color ("Color", Color) = (1,1,1,1)
        _Blend ("Texture Blend", Range(0,1)) = 0.0
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Test ("Test", Float) = 0.0

        _NoiseTex("Noise Texture", 2D) = "White" {}
    }


 void surf (Input IN, inout SurfaceOutputStandard o)
    {


fixed4 c  = lerp(tex2D (_RockInnerShallow, IN.uv_RockInnerShallow),
                 tex2D (_RockInnerDeep, IN.uv_RockInnerDeep), rockDepthT) * _Color;

   o.Albedo = c.rgb;
   o.Alpha = c.a;

This last bit is the lerping part.

Thanks.