The Dog Leash only works for random battles. It doesn`t work for Event and Boss battles. Anything battle without Gun Blaze(Normal battle theme) is an event battle. The purification of a save point is an event battle even if your location is randomized for it.
Rana Rex : This... this is madness ! What will become of my... my garden ? My flowers ? Agan : I`m sure they`ll be fine. They have your corpse to feed on now.
^This. And get better at the game. Stop depending on guides so much and just figure out strategies on your own. It'll be far more satisfying to beat it on something you think up rather than something you read.
And don't worry about reading a FAQ to miss stuff. You'll be able to backtrack to every dungeon you left except for maybe two of them. At the worst, just search the boards for a "missables" faq or thread. I'm like you where I don't like to miss anything but I don't want to obsessively check a guide which will inevitably have spoilers. Most folks will mention missables so get a list of JUST those.
Also, you'll get a "detector" item that will make a noise if you miss a treasure so you can go back to old dungeons to find anything you miss....just run into a room and use it and you'll find what you missed. You'll also get an item in the final dungeon that makes secret chests and platforms show up in some dungeons so you'll have to backtrack to some dungeons anyway.