[openbox] send window to top only once

[阿四]

Hi all,
In my openbox configuration, I've binded the key "C-A-t" to start a
terminal like this:

<keybind key="C-A-t">
   <action name="Execute">
      <command>lxterminal</command>
   </action>
</keybind>

However, this doesn't work as I hope. I want it execute the lxterminal
application and send this window to top layer(only once, not always).
I've read the help:actions on openbox wiki.And still haven't found
action work as I hope. The action:

<action name="SendToLayer"><layer>top</layer></action>

also doesn't work, it set window "Always on Top", which is not I want.

Regards.