diff --git a/message_definitions/v1.0/common.xml b/message_definitions/v1.0/common.xml
index f657bf8e33..713c76ffa3 100644
--- a/message_definitions/v1.0/common.xml
+++ b/message_definitions/v1.0/common.xml
@@ -314,20 +314,30 @@
     </enum>
     <!-- fenced mode enums -->
     <enum name="FENCE_ACTION">
+      <description>Actions following geofence breach.</description>
       <entry value="0" name="FENCE_ACTION_NONE">
-        <description>Disable fenced mode</description>
+        <description>Disable fenced mode. If used in a plan this would mean the next fence is disabled.</description>
       </entry>
       <entry value="1" name="FENCE_ACTION_GUIDED">
-        <description>Switched to guided mode to return point (fence point 0)</description>
+        <description>Fly to geofence MAV_CMD_NAV_FENCE_RETURN_POINT in GUIDED mode. Note: This action is only supported by ArduPlane, and may not be supported in all versions.</description>
       </entry>
       <entry value="2" name="FENCE_ACTION_REPORT">
         <description>Report fence breach, but don't take action</description>
       </entry>
       <entry value="3" name="FENCE_ACTION_GUIDED_THR_PASS">
-        <description>Switched to guided mode to return point (fence point 0) with manual throttle control</description>
+        <description>Fly to geofence MAV_CMD_NAV_FENCE_RETURN_POINT with manual throttle control in GUIDED mode. Note: This action is only supported by ArduPlane, and may not be supported in all versions.</description>
       </entry>
       <entry value="4" name="FENCE_ACTION_RTL">
-        <description>Switch to RTL (return to launch) mode and head for the return point.</description>
+        <description>Return/RTL mode.</description>
+      </entry>
+      <entry value="5" name="FENCE_ACTION_HOLD">
+        <description>Hold at current location.</description>
+      </entry>
+      <entry value="6" name="FENCE_ACTION_TERMINATE">
+        <description>Termination failsafe. Motors are shut down (some flight stacks may trigger other failsafe actions).</description>
+      </entry>
+      <entry value="7" name="FENCE_ACTION_LAND">
+        <description>Land at current location.</description>
       </entry>
     </enum>
     <enum name="FENCE_BREACH">
@@ -2027,6 +2037,7 @@
         <param index="6" label="Longitude">Longitude</param>
         <param index="7">Reserved</param>
       </entry>
+      <!-- value 4005 reserved for MAV_CMD_SET_FENCE_BREACH_ACTION (see development.xml). -->
       <entry value="5100" name="MAV_CMD_NAV_RALLY_POINT" hasLocation="true" isDestination="false">
         <description>Rally point. You can have multiple rally points defined.
         </description>
diff --git a/message_definitions/v1.0/development.xml b/message_definitions/v1.0/development.xml
index 3413568f57..9380b0751b 100644
--- a/message_definitions/v1.0/development.xml
+++ b/message_definitions/v1.0/development.xml
@@ -44,6 +44,25 @@
         <description>Synthetic/calculated airspeed.</description>
       </entry>
     </enum>
+    <!-- The MAV_CMD enum entries describe either: -->
+    <!--  * the data payload of mission items (as used in the MISSION_ITEM_INT message) -->
+    <!--  * the data payload of mavlink commands (as used in the COMMAND_INT and COMMAND_LONG messages) -->
+    <!-- ALL the entries in the MAV_CMD enum have a maximum of 7 parameters -->
+    <enum name="MAV_CMD">
+      <description>Commands to be executed by the MAV. They can be executed on user request, or as part of a mission script. If the action is used in a mission, the parameter mapping to the waypoint/mission message is as follows: Param 1, Param 2, Param 3, Param 4, X: Param 5, Y:Param 6, Z:Param 7. This command list is similar what ARINC 424 is for commercial aircraft: A data format how to interpret waypoint/mission data. NaN and INT32_MAX may be used in float/integer params (respectively) to indicate optional/default values (e.g. to use the component's current yaw or latitude rather than a specific value). See https://mavlink.io/en/guide/xml_schema.html#MAV_CMD for information about the structure of the MAV_CMD entries</description>
+      <entry value="5005" name="MAV_CMD_SET_FENCE_BREACH_ACTION" hasLocation="false" isDestination="false">
+        <wip/>
+        <!-- This message is work-in-progress and it can therefore change. It should NOT be used in stable production environments. -->
+        <description>Sets the action on geofence breach.
+          If sent using the command protocol this sets the system-default geofence action.
+          As part of a mission protocol plan it sets the fence action for the next complete geofence definition *after* the command.
+          Note: A fence action defined in a plan will override the default system setting (even if the system-default is `FENCE_ACTION_NONE`).
+          Note: Every geofence in a plan can have its own action; if no fence action is defined for a particular fence the system-default will be used.
+          Note: The flight stack should reject a plan or command that uses a geofence action that it does not support and send a STATUSTEXT with the reason.
+        </description>
+        <param index="1" label="Action" enum="FENCE_ACTION">Fence action on breach.</param>
+      </entry>
+    </enum>
   </enums>
   <messages>
     <message id="53" name="MISSION_CHECKSUM">