How to detect if object is within another object?

I am instantiating objects above my scene and then raycasting them down into position on the ground, and I have attempted to make a script which would remove any objects that are overlapping. It does not seem to work because sometimes the objects will still overlap. Here is my code:

  `public class spawnChecker : MonoBehaviour {
     // Use this for initialization
     void Start () {
         obstacleSpawner obstacleSpawner = gameObject.GetComponentInParent<obstacleSpawner> ();
         RaycastHit hit;
         Vector3 down = new Vector3 (0, -1, 0);
         transform.rotation = Quaternion.Euler (14, 0, 0);
         if (Physics.Raycast (transform.position, down, out hit, Mathf.Infinity)) {
             if (hit.transform.tag == "Ground") {
                 Vector3 newLocation = hit.point;
                 newLocation += new Vector3 (0, transform.localScale.y / 2, 0);
                 transform.position = newLocation;
                 CheckBounds ();
                 if (CheckBounds() == false) {
                     obstacleSpawner.spawn (1);
                     Destroy (gameObject);
                 }
             } else {
                 obstacleSpawner.spawn (1);
                 Destroy (gameObject);
             }
         } else {
             obstacleSpawner.spawn (1);
             Destroy (gameObject);
         }
     }
     
     public bool CheckBounds()
     {
         
         Bounds objectBounds = (gameObject.GetComponent<MeshFilter>().mesh.bounds);
 
         float sqrHalfObjectSize = objectBounds.extents.sqrMagnitude;
         //float overlapingSphereRadius = Mathf.Sqrt (sqrHalfObjectSize + sqrHalfObjectSize);
         Collider[] hitColliders = Physics.OverlapBox(transform.position,objectBounds.extents,transform.rotation,1 << 8);
         foreach(Collider otherCollider in hitColliders)
         {
             if (otherCollider.bounds.Intersects (objectBounds))
                 return (false);
         }
         return (true);
 
 }
 }
 `

Would I be better off using OnCollission methods? P.S., I have checked the bounding boxes for the mesh's and they are all in order, so what is going wrong?