--- ad.module.orig	2012-04-19 23:19:45.897935925 +0200
+++ ad.module	2012-04-19 23:36:10.601917908 +0200
@@ -577,6 +577,10 @@ function ad_access($op, $node, $account)
           !user_access('administer advertisements', $account)) {
         return false;
       }
+      // Disable show directly the ad node page to simple users
+      if (arg(0)=='node' && arg(1)==$node->nid && !user_access('administer advertisements', $account)) {
+        return false;
+      }
   }
 }