diff --git a/ArduSub/fence.cpp b/ArduSub/fence.cpp
index 1b46a89a43..66ed66d959 100644
--- a/ArduSub/fence.cpp
+++ b/ArduSub/fence.cpp
@@ -8,19 +8,18 @@
 // called at 1hz
 void Sub::fence_check()
 {
-    uint8_t new_breaches; // the type of fence that has been breached
-    uint8_t orig_breaches = fence.get_breaches();
-
-    // check for a breach
-    new_breaches = fence.check_fence(current_loc.alt/100.0f);
-
-    // return immediately if motors are not armed
+    // ignore any fence activity when not armed
     if (!motors.armed()) {
         return;
     }
 
+    const uint8_t orig_breaches = fence.get_breaches();
+
+    // check for new breaches; new_breaches is bitmask of fence types breached
+    const uint8_t new_breaches = fence.check();
+
     // if there is a new breach take action
-    if (new_breaches != AC_FENCE_TYPE_NONE) {
+    if (new_breaches) {
 
         // if the user wants some kind of response and motors are armed
         if (fence.get_action() != AC_FENCE_ACTION_REPORT_ONLY) {
@@ -44,10 +43,8 @@ void Sub::fence_check()
 
         // log an error in the dataflash
         Log_Write_Error(ERROR_SUBSYSTEM_FAILSAFE_FENCE, new_breaches);
-    }
-
-    // record clearing of breach
-    if (orig_breaches != AC_FENCE_TYPE_NONE && fence.get_breaches() == AC_FENCE_TYPE_NONE) {
+    } else if (orig_breaches) {
+        // record clearing of breach
         Log_Write_Error(ERROR_SUBSYSTEM_FAILSAFE_FENCE, ERROR_CODE_ERROR_RESOLVED);
     }
 }