Legalities on copying DVDs?

I have searched through most of the previous questions asked on this subject but never seen anyone provide a link to a site that shows it is legall to copy your own dvd or cd that you paid big bucks for. i have also searched the copyright groups for home use burning and still not finding anything in writing.I have been copying for years and i am close to 60 years old and can go back to the days of everyone copying their rare vinyl records to the reel to reel tape recorders to preserve the records that eventually fail due to being played too much. Then the cettes came and then the vcrs and now the dvds. When i go out and pay big bucks for a rare or hard to get dvd or a triology boxed set i burn them and only watch the copies so i can preserve my investment in case they get scratched and especialy as i live in Australia and i have lost qite a few in summer months by having them in my car and they have warped from the heat.I suppose this is a tricky question as it depends on which country we live and also different state laws, but has anyone found a site that clearly says it is legal for us to preserve (for the better word) our treasured dvds or music.?.Its kinda like saying we cant carry a spare wheel in our cars in case we get a flat.