Proper Way to Implement Jump for Character

Hi, I am currently trying to add a jump function to my "PlayerMovement" script. It works fine as far as jumping goes, but I noticed that I can jump on things that I shouldnt be able to(sides of walls, for example)

I know that it has to do with the OnCollisionStay and Exit functions, but I cant figure out what to replace them with to make it work, I have had to resort to using a tag to forbid the player from being able to jump on certain objects, but it makes things more of a hassle than anything

Here is my code! Any help would be greatly appreciated! Thanks again!

 var direction : Vector3 = new Vector3(0,0,0);
 var Speed : float = 0.0;
 var gravity : float;
 var jumpSpeed : float;
 var letJump = false;
 var letMove = true;
 var jumpSound : AudioClip;
 var target : Transform;
 
 function Jump()
 {
     if(letJump)
     {
         if (Input.GetKey(KeyCode.Space))
             {    
                 audio.PlayOneShot(jumpSound);
                 rigidbody.AddForce(0, jumpSpeed, 0);            
             }
     }
 }
 
 function OnCollisionStay(other : Collision)
 {
     if(other.gameObject.tag == "NoJump")
     {
         Debug.Log("Cant Jump Here!");
         letJump = false;
     }
     
     if(other.gameObject.tag != "NoJump")
     {
     letJump = true;
     }
 }
 
 function OnCollisionExit(col : Collision)
 {
     letJump = false;
 }
 
 function Update()
 {
     if (letMove == true)
     {
         direction.x = Input.GetAxis("Horizontal");
         direction.z = Input.GetAxis("Vertical");
     }
     
     direction.Normalize();
     rigidbody.AddForce( direction * Speed );
 
     direction.y -= gravity * Time.deltaTime;
         
     if(Input.GetButtonDown("Jump"))
     {
         Jump();
     }
     
     if(Input.GetButtonUp("Jump"))
     {
         direction.y -= gravity;
     }
 
 }