cheap and easy epoxy

What is the easiest way to secure my rocks to each other while they can still be in my tank with my fish? I am starting to add more base rock to my tank and until now i have not been worried about it falling because it was not being stacked very high. I want to be able to build a tower so the top half of my tank has something for my fish to swim around. the rocks in my picture are about the only size i can get so i want to connect a couple together to make a good base. cheap is best but any input would be great! thanks in advance.

 

You can build the towers outside of the tank, and then place them back in the tank. Wet stacking rock is not a good thing.

 

Will i be able to put it together while it is wet outside the tank. some of that is new base rock but the rest of it is live rock and i cant let it dry out.