No, you can have fish in the basement, as most fish rooms are located.The only way to be 100% flood proof is to not keep fish lol
I have two big tanks, a 75 and 125, on 2nd floor living area. So I have zero tolerance of flooding. You can implement operational precautions or design to contain minor spills, but not flooding from major leak or slow leak overnight or vacation.
I will pay attention to design first. Avoid filtration system that has design vulnerability such as external plumbing that can leak. Avoid buying used big tanks even at bargain price.
Next, pay attention to WC. A 5 min overfill can dump a lot of water. I do 75% WC weekly on my upstairs tanks, so the risk is high. I use a timer to warn against overfilling.