hi dan, the lighthood corners are mitred with a half inch scollop taken out of all the visiable edges takes the emphasis(spelling) off the corner and gives the look of a panelled surface.some people call them feature edges.
the rocks are all just sitting there didnt use silicon or anything just placed them.(didnt fancy trying to catch fish around them)put them in over the course off a day if it was too unstable pulled them out and started again hense why it took all day to set up.it is really stable it takes a bit of effort to move them. i put the bottom row on a piece off poly cut to fit between the braces then put in the gravel around them.so if the fish play bulldozers(which they have )the rocks wont come down.as for putting holes in the stones the only thing i found that works was a masonary bit. i found some of the tall background today the rockface one it looks heaps better now no hoses, your new 740 litre tank sounds awesome what r u going to put in it?
hope this helps , glenn