i would take the small rock and use supper gule and glue to a larger rock and let time do the job ,as i think part of your yuma is deteched , once it is touching on the bigger rock, it feels comfortable, it will shift and the whole yuma will be attached there, Hopefully*.
During this process, let it be in low flow area..if not really will be blown away..
Dun use suppergule directly on the yuma itself, i tried that ones ,it attached to the rock, but eventually ,somehow, it melted away...
Hope your yuma do attached.