Best way to keep an ai grounded?

Hi so right now I have a basic script that patrols waypoints and follows and attacks a player when it gets near. I have a script that tries to keep it grounded but it is buggy and doesn't work all the time. I was wondering what's the best way to keep the ai on the ground.

 var waypoint : Transform[]; // The amount of Waypoint you want
 var patrolSpeed : float = 3;       // The walking speed between Waypoints
 var loop : boolean = true;       // Do you want to keep repeating the Waypoints
 var player : Transform;          // Referance to the Player
 var dampingLook = 6.0;          // How slowly to turn
 var pauseDuration : float = 0;   // How long to pause at a Waypoint
 var attackRange = 10;          // Range to start the attack
 var attackSpeed = 5.0;          // Speed to attack
 var attackLook = 10.0;          // How fast to turn when attacking
 var ASpeed = 1;
 
 private var distanceToPlayer : int; // Distance from the enemy to the Player
 private var currentTime : float;
 private var currentWaypoint : int = 0;
 private var character : CharacterController;
 private var gravity : float = 2.0;
 private var attacking : boolean = false;
 private var isattacking : boolean = false;
 private var captured : boolean = false;
 
     function Awake(){
 
     }
     
     function Start(){
         character = GetComponent(CharacterController);
         animation["bite"].speed = ASpeed;
         animation["bite"].layer = 1;
     }
     
     function Update(){
         // Gets the distance between the enemy and the Player    
         distanceToPlayer = Vector3.Distance(player.position, transform.position);
         if(captured){
              animation["Death"].wrapMode = WrapMode.ClampForever;
              animation.Play("Death");
            }
         else if(distanceToPlayer < attackRange){
            attacking = true;
            attack();
            }else{
            attacking = false;
            }
             if(currentWaypoint < waypoint.length && !attacking && !captured){
                patrol();
                }else{    
                 if(loop && !attacking){
                    currentWaypoint=0;
                 } 
             }
     }
     function patrol(){
         var target : Vector3 = waypoint[currentWaypoint].position;
         target.y = transform.position.y; // This keeps the waypoint at character's height
         var moveDirection : Vector3 = target - transform.position;
         if(moveDirection.magnitude < 0.5){
            if (currentTime == 0) {
              currentTime = Time.time; // Pause over the Waypoint
              animation.Play("idle");
            }
            if ((Time.time - currentTime) >= pauseDuration){
              currentWaypoint++;
              currentTime = 0;
            }
         }else{        
             // This gets the location of the waypoint and rotates the AI to look at the waypoint and dampen the rotation
            var rotation = Quaternion.LookRotation(target - transform.position);
            transform.rotation = Quaternion.Slerp(transform.rotation, rotation, Time.deltaTime * dampingLook);
            moveDirection.y = 0;
            moveDirection.y -= gravity; //Gravity so the the AI  stays on the ground
            character.Move(moveDirection.normalized * patrolSpeed * Time.deltaTime);
            animation.Play("trot");
         }  
     }
  
     function attack(){
         // Attack the Player
         if (distanceToPlayer <= 2) {
             animation.Play("bite");
         } else {
         animation.Stop("bite");
         // Rotate to face the Player
         var lookPos = player.position - transform.position;
             lookPos.y = 0;
         var rotation = Quaternion.LookRotation(lookPos);
             transform.rotation = Quaternion.Slerp(transform.rotation, rotation, Time.deltaTime * attackLook);
         // Move towards the Player
         var target : Vector3 = player.position;
         var moveDirection : Vector3 = target - transform.position;
         moveDirection.y = 0; // This helps stop the AI running up off the floor to match the Players Y axis
         moveDirection.y -= gravity; //Gravity so the the AI always stays on the ground
         character.Move(moveDirection.normalized * attackSpeed * Time.deltaTime);
         animation.Play("run");
         }
     }
     
     function OnCollisionEnter(collision : Collision){
         if(collision.gameObject.tag == "Projectile"){
             captured = true;
         }
     }