Some woods are brittle and more prone to breaking at a place that is small in size, longer in length, and cross-grained. The Box Elder I recently used on some small crosses recently seemed to be a good choice. Anything you coat them with that can soak in a bit will help strengthen the weaker places. A couple coats of spray polyurethane or just a thin coat of liquid CA adhesive on the backside will help. Some of my crosses were 1/4" thick and are holding up well. Another style were cut from a 3/8" thick sheet.