Something weird is happening with my vertex shader...

Hi!

I'm quite new to programming shaders, so I'm still learning. I was trying to create a shader that reproduces a "Fisheye Lens" effect, similar to one found in an old cancelled game calledSonic Xtreme. While I got the effect working somewhat well, I got some weird artifacts going on. Example here: https://gyazo.com/5f13465fe8598d27ae87667aaa41de14

Here's the shader:

 Shader "Mars/Surface" {
     Properties {
         _Color ("Color", Color) = (1,1,1,1)
         _MainTex ("Albedo (RGB)", 2D) = "white" {}
         _Glossiness ("Smoothness", Range(0,1)) = 0.5
         _Metallic ("Metallic", Range(0,1)) = 0.0
         _Depth ("Depth", Float) = 10
         _Range ("Range", Range(0,1)) = 0.1
     }
     SubShader {
         Tags { "RenderType"="Opaque" }
         LOD 200
         
         CGPROGRAM
         // Physically based Standard lighting model, and enable shadows on all light types
         #pragma surface surf Standard fullforwardshadows vertex:vert
 
         // Use shader model 3.0 target, to get nicer looking lighting
         #pragma target 3.0
 
         sampler2D _MainTex;
         float _Depth;
         float _Range;
 
         struct Input {
             float2 uv_MainTex;
             half4 color : COLOR;
             float4 pos : SV_POSITION;
         };
 
         half _Glossiness;
         half _Metallic;
         fixed4 _Color;
 
         void vert(inout appdata_full v, out Input o)
         {
             UNITY_INITIALIZE_OUTPUT(Input,o);
 
             o.color = v.color;
 
             v.vertex.z *= 2;
 
             float horScale = cos((v.vertex.x - _WorldSpaceCameraPos.x) * _Range);
             float verScale = cos((v.vertex.y - _WorldSpaceCameraPos.y) * _Range);
 
             v.vertex.z += abs((horScale * _Depth
                 + verScale * _Depth - _Depth * 2));
 
             o.pos = UnityObjectToClipPos(v.vertex);
             //o.uv = TRANSFORM_TEX(v.uv, _MainTex);
             
             //v.vertex.x -= horScale;
             //v.vertex.y -= verScale;
         }
 
         void surf (Input IN, inout SurfaceOutputStandard o)
         {
             // Albedo comes from a texture tinted by color
             fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
             o.Albedo = c.rgb * IN.color;
             // Metallic and smoothness come from slider variables
             o.Metallic = _Metallic;
             o.Smoothness = _Glossiness;
             o.Alpha = c.a;
         }
         ENDCG
     }
     FallBack "Diffuse"
 }
 

Hope anyone can help me out here. :)

Thanks!