Hi Chimpzoo.
Blip, who's indoor / outdoor, came to us from a rescue seven years ago and had been indoors there for six months, and possibly all her life. We kept her in for about six weeks after her arrival, then started letting her out into the back garden under supervision. We gradually let her wander a little bit more each day and after a few weeks, gave her free access during the day.
This worked for us, but I would think it depends how long your pud has been indoor-only. How old is s/he and what is his / her background?
What's pud's name, by the way?