How to apply more than one trigger on a single gamebject

I'm wanting to add more than one trigger on a single game object in different areas of the prefab. Should i use 3 box colliders? Can it be done? Please give me guidance regarding this.

I have run into a dead end by trying this approach:

I have 3 spawners spawning 2 prefabs vertically down. The spawning starts just above the view and when the object(moving down)exits the view...it re-spawns: My problem is that the 2 spawning objects in the array overlaps. Screen size = 768x1024.....objects Size = 256x170.666667. In other words....3 objects x 6. I'm trying to either fix this...or go the other route..as above mentioned.

var enemies :GameObject[]; // Array of enemy prefabs. tag names go here var spawnTime :float = 1.0f; // The amount of time between each spawn. var spawnDelay :float = 1.0f; // The amount of time before spawning starts. var enemySpeed :float = 5.0f;
var spawn :boolean = false; var spawnPosition :Transform; var randomLocation :Vector3; var enemyIndex :int;

function Start() {

     // Start calling the Spawn function repeatedly after a delay .
     InvokeRepeating("Spawn", spawnDelay, spawnTime);
     
     spawn = true; // make sure Invoke started only once
     randomLocation = Random.insideUnitSphere * 2; //2 is radius
     randomLocation.y = 0.0f;

} function Spawn () { // Instantiate(spawnObject[spawnObjectIndex],spawnPosition.position + randomLocation,spawnObject[spawnObjectIndex].transform.rotation);

     // Instantiate a random enemy.
     enemyIndex = Random.Range(0, enemies.Length);

     Instantiate(enemies[enemyIndex], transform.position, transform.rotation);

}

function Update () {

 amtToMove = enemySpeed * Time.deltaTime;

 transform.Translate(Vector3.down * amtToMove);
 
 if(transform.position.y <=-6)            //when object reaches bottom of the view 
 {
 
 transform.position.y = 6;               // back to top of the view
 enemySpeed *= 1.02f;            // increase my spawn speed with every cycle
 
 }