Your snake shouldn't be kept on the floor anyway so the dog shouldn't be a problem. As for the tubs security, buy the ones with lid locks. A tub with locking lid is probably 89% less likely to be escaped from than a traditional 20 gallon tank with mesh lid. i would say get a locking lid sterilite tub and you will be so glad you didn't switch to a tank. Tanks are not only easier to escape from they are also harder to clean. Tubs on the other hand can be easily lifted and sanitized while a 20 gallon is bulky and heavy making cleaning harder and more of an unpleasant chore