(vl-load-com)

(defun c:FOO (/ *error* acDoc oBlocks blockName oLayers layerName
              layersToLock
             )

  (defun *error* (msg)
    (foreach x layersToLock
      (vla-put-lock x :vlax-true)
    )
    (if acDoc
      (vla-endundomark acDoc)
    )
    (cond ((not msg))                                                   ; Normal exit
          ((member msg '("Function cancelled" "quit / exit abort")))    ; <esc> or (quit)
          ((princ (strcat "\n** Error: " msg " ** ")))                  ; Fatal error, display it
    )
    (princ)
  )

  (if (ssget "_x" '((0 . "INSERT")))
    (progn
      (vla-startundomark
        (setq acDoc (vla-get-activedocument (vlax-get-acad-object)))
      )
      (setq oBlocks (vla-get-blocks acDoc))
      (setq oLayers (vla-get-layers acDoc))
      (vlax-for x (vla-get-activeselectionset acDoc)
        (if (= :vlax-true
               (vla-get-isxref
                 (vla-item
                   oBlocks
                   (setq blockName (strcase (vla-get-effectivename x)))
                 )
               )
            )
          (progn
            (setq oLayer
                   (vla-add oLayers
                            (setq layerName (strcat "_XREF-" blockName))
                   )
            )
            (if
              (and
                (= :vlax-true
                   (vla-get-lock
                     (setq oLayer (vla-item oLayers (vla-get-layer x)))
                   )
                )
                (not (vl-position oLayer layersToLock))
              )
               (progn
                 (setq layersToLock (cons oLayer layersToLock))
                 (vla-put-lock oLayer :vlax-false)
               )
            )
            (vla-put-layer x layerName)
          )
        )
      )
    )
  )
  (*error* nil)
)