Coral-Shop, the equipment manufacturer from the Czech Republic, recently released two compounds to mount stone to both other stones and glass. The bonding agents are meant to be used dry and will provide strong and reef safe bonds while setting up your aquarium.
The CS Reef Bond STS bonds stone-to-stone and is a one-part component that just mixes with water. Once mixed up to a paste-like consistency, Reef Bond STS give you 45 minutes to set your stone in place. Once it hardens after 48 hours, it provides a bond that will strengthen over time and will not breakdown in water. We assume that after the 48 hours, it is safe to put the stone in water without having to worry about alkaline and other products leaching from the bond into the tank.
The CS Reef Bond STG looks like a really nifty product that allows you to adhere rock directly to glass. The two-part mix is water resistant and maintains 40% elasticity even when fully cured. Starting with a smooth surface on the stone clean of dust and dirt (and if you need too, you can fill gaps with the CS Reef Bond STS) you mix the two products and apply in a 1 cm layer and hold against clean, grease-free glass until it bonds. Let cure at least 48 hours and then add water.
Although off-the-shelf products work well, we are often left with leaching byproducts or weak bonds. If these products perform as advertised, you could do some impressive aquascaping.