How to get dried gum off the bottom of a shoe (with imprints on sole, not flat)?

My son has gum on the bottom of his shoe, only his shoe is not flat sole it has different designs on the bottom so its stuck in the spaces. I found out the gum has been there for about a week and so it is dry and old and has rocks and stuff all stuck in it. I have tried to use goo gone and sc it...not working. What else can I do?