This is just one more way to hide the ring and I leave the proposal up to you. Take an Altoids container, a mini works well. Open it, place ring inside. You could also cut foam out to fit snugly inside to hold the ring. Ask her if she wants a mint perhaps or just keep it safe from muggers who would not take your mints. I leave the details and fanciful notions up to you.
This is one of my first instructables, extremely easy and requiring no pictures actually but one would do. I must have chosen the wrong style becasue it is making me do multiple pi