There are many environmentaly safe stripper for decks on the market, buy one of good quality and apply it liberally to the deck. Make sure that you aallow it ample time to work and then you can power wash it off. You may need to repeat the process on stubborn spots. Once you have it all off I recommend using a wood conditioner that opens up the grain to allow for deep penetration of the stain. For the new deck that you want to stain. I personally like to let decks sit for a year before coating them, however if you cannot wait then I would use a mill glaze remover and conditioner to open up the grai of the wood. I have done many successfull deck projects and will only do it one way. Take a semi transparent oil based deck stain and thin it out 35 - 40% with mineral spirits or varsol and apply one coat only. This will colour the deck and protect it and never ever peel or need to be stripped. When you notice it needs to be redone simply wash it off and coat it again. You will be able to see the grain and it will not look like paint. I live in Canada and have a pool by my deck that has kids getting in and out all summer long, then it see a very serious winter and all the various seasons in between. Here in theseconditions I have to recoat it every 2-3 years. If I were in a more temperate climate I don't know how long it would last. Alot longer I would guess.