All of my rocks are painted with quality acrylic paint and sealed with indoor/outdoor varnish. Any thing exposed to the elements outside are subject to damage resulting from the hot direct sun and/or freezing temperatures. (just like the paint on your home.) In order to preserve your rock I recommend that they be placed in a nice shaded area with little exposure to the beating sun. If you live in an area that has freezing temperatures then it would be best to bring your rock inside.These rocks are easy to clean, when needed. Just wash them with warm soapy water and a soft cloth. Some varnishes tend to lose their "shine" after time so it is helpful to clean the rock, dry it well and spray it (outdoor project obviously), with a good indoor/outdoor non-yellowing varnish. (I have good results with rustoleum clear gloss.) Not all varnishes are created equal so I stick to what works for me.  :)