Car body filler (bog) is great for gluing stones and concrete. It can be used for mending garden gnomes or making things from beach pebbles.
Unfortunately, it is very fast setting. The green layer of this flower was assembled on a sheet of plastic and then quickly glued. The petals were positioned using plasticene before gluing. The leaves were painted before putting on the petals. The centre stone was attached with thick acrylic gel and painted with thin acrylic gel. For exterior use, it should be sprayed with clear acrylic car gelcoat. This will provide UV protection and help the paint to last longer.