I found some nice looking, inexpensive plastic plants on line. These are not intended for aquariums - but for floral arrangments. They are 100% plastic, no internal wire, and they look very realistic. Now I'm considering what to use to mould a base to secure the stems in an upright position and weigh them doen into the water. I need a cement or glue which is heavy, which will grip the plant stems when it dries, but most important - that won't pollute the water or harm the fishes. Any ideas?