Anyone can make a metaphor. We do it all the time. For instance, we say things like ‘I’ll cross that bridge when I come to it’ when we want to delay handling an issue, or ‘muddying the water’ when someone is trying to complicate an argument.
Metaphors borrow something tangible or easily understood to represent something intangible or difficult to express. Of course there has to be some thread of commonality — some sense in which this ‘borrowing’ is able to supply meaning.
For instance, you can’t successfully speak of ‘the orange rind of peace’, because there’s no way in which the peel of a round orange fruit can be used to express harmonious coexistence.
By contrast, ‘the mouse of peace’ does have a germ of usefulness. But I don’t suggest you attempt to use ‘the mouse of peace’ as a literary metaphor, because ‘peace’ is a concept that draws its power from the great seriousness of war, while mice are small and prone to form plagues. On the other hand your intention might be comical, in which case go ahead. (Collapsing ‘levels’ like this — pairing the ridiculous with the sublime — is a staple of comic writing.)
Remember, when crafting a metaphor, it pays not to be too obvious. For instance, speaking of ‘mouse of peace’:
‘The crowd’s roar turned to a soft squeak after McCap finished his speech. Gradually figures began to scurry back into their tenement holes, leaving McCap on the podium feeling like an unhungry cat.’
Did you gain the sense there were mice in that place? I did, even though ‘mouse’ wasn’t used. In fact I felt positively overrun.
Carrying a metaphor over several phrases or sentences creates an ‘extended’ metaphor; but it’s easy to overdo. In the above paragraph so many indicators point to ‘mice’ that a reader can feel like jumping on a chair. But you can always prune some of the mouse-related terms out:
‘The crowd’s roar quietened after McCap’s speech. Gradually figures began to scurry away from the podium, leaving McCap feeling like an unhungry cat.’
Crafting metaphors in subtle ways is fun, a bit like playing peek-a-boo with ideas. Show too much, and the whole thing collapses under its own weight. Show too little, and the metaphor doesn’t have any effect at all. But show just enough and the reader ‘sees’ things in a fresh way.
And best of all there’s no muddying the water!