Gnome Garden - Specialty Paints that will hold up to the environment

I am going to use these "Hulk" hands in our Gnome Garden to create a type of cave opening for the Gnomes to go into.  One of my thoughts was to use stone spray paint to create the "rock look" and then touch up by hand to add shadowing and color changes.  Would this paint hold up outside if I use a "poly" on it.  If not, I'll probably go with a cement cover, but I thought painting would be easier.