Military order that would be safer with a guard in place? (4,4)

I believe the answer is:
open fire
'guard in place?' is the definition.
The definition and answer can be both related to competing as well as being verbs in their base form.
Perhaps there's an association between them I don't understand?
'military order that would be safer' is the wordplay.
I cannot really see how this works, but
'military' could be 're' (Royal Engineers) and 're' is found in the answer.
'order' could be 'o' (abbreviation e.g. in British honours OM, OBE etc.) and 'o' is present in the answer.
This explanation may well be incorrect...
'with a' is the link.
Can you help me to learn more?
(Other definitions for open fire that I've seen before include "Source of heat" , "Homely feature of room" , "Perhaps start sniping" , "army command" , "order for soldiers?" .)
