Why not use them standing upright that is so that the holes in the brick are next to each other and not exposed to snails and spiders making a home in it.
The borders, of course. If there's little holes in the bricks you can plant some mini flowers here and there in the holes. Make custom sized raised beds in back of garden as additional focal points to make plants in rear look taller and provide that background to plant against towards the front of beds.
Here is a post I just published today... DIY Brick Edging... it's my favorite way to use brick in the garden!!