Either order seems OK to me when, as in the example, it is an appeal to a higher power for the thing desired.
Otherwise, 'only' should really come before the thing qualified. I only saw him last night (I did not speak to him)
I saw only him last night (No-one else)
I saw him only last night (that recently)
The trouble is that, in speech, we tend to emphasise the thing to which only relates rather than placing only correctly.
I only SAW him last night
I only saw HIM last night
I only saw him LAST NIGHT
In short notices, only is likely to come last: Staff Only.