Here is a link that might help with the algae
Algae problems in aquariums

On securing the rocks in the terrarium I think you have to glue them in place. But check out and contact those with email addresses for their approach
Dutch Vivariums

Would I use an animal-safe silicone sealant for that, or what?
Thanks,
-Jmcat

http://www.arachnoboards.com/ab/showthread.php?p=1139331
At Arhnaboard forum Liquid Nail is used
use the link above for more info

Hmmm, unfortunately, I just saw on their website: "Liquid Nails products will resist water penetration. None of our products should be used below the waterline or immersed in water for long periods of time (i.e. pools, aquariums)." That could be a problem. Also, I'd like to be able to find whatever I end up using locally, rather that ordering it. Do you think that one of the local "very-friendly-people-trying-to-sell-you-something" at Ace Hardware or Home Depot would be able to direct me to something they carry that would hold well, stand being submersed, and be frog-safe?
Thanks,
-Jmcat

you can occasionally water using physan 20. but it's not suitable option if you plan to keep animals -- fine for plants, toxic for aquatic animals.

For the algae: Orchid and hydroponic suppliers sometimes stock a special herbicide, which will only harm the algae and nothing else.

For keeping the rocks in place: Just use ordinary Aquarium silicon, it works a charm!!!