If you've got a stinky pair of shoes, a custom made cat litter deodoriser will suck up all the moisture and help neutralise the odour.
Your shoes get smelly because the moisture in your shoes allows odour-causing bacteria to thrive. The HouseholdHacker YouTube channel demonstrates, among other methods, how you can combat the stench of your favourite sneakers with some products you might be able to find at home.
Sometimes you need to go with tough stuff like rubbing alcohol, but if it's not too intense you can create a simple deodoriser. Pour a little cat litter — silica-based if you have it — into an old stocking or sock and wrap it up. Stuff one into each shoe and it will dry them up while adding a nice little cover scent. Just make sure there aren't any holes in the stockings or socks. Nobody wants a bunch of tiny rocks in their shoes.
10 Ways to Stop Shoe Odor! [YouTube]