FFS DO NOT try Gumtree. It's a haven for puppy farmers and arseholes.
The last poster on here who did so ended up with her neighbours small child bitten and the dog put to sleep within 48 hours of taking him on from a Gumtree advertiser.
You take a dog from the free ads and you have no fucking idea what you're bringing into your home. People will tell you what you want to hear. You'll end up with a totally unassessed dog which has no-where to go if it doesn't wa=ork out... after all, the seller is hardly likely to take him back is he? You may end up with a dog who howls as soon as you leave him, who shreds your furniture, who pees on your floor... none of that is insurmountable but it's not funny if you have no support from a dog expert.... or you may even end up with someone hurt.
Please - approach a reputable rescue. Remember that their dogs will all be assessed professionally before being rehomed and that many rescue dogs come from family homes as a result of divorce, unemployment etc etc - rescue dogs are far from being nothing but unknown strays.
And, even when a dog comes from a family, we don't just take the previous owner's word for it (as I said, people lie... and, btw, if they do so to rescue what the feck do you think they will try to do with the average Joe Public?). Rescue will thoroughly and responsibly assess their dogs and match them to suitable homes (and vice versa!) regardless of how much the previous owner sings their dog's praises.
A dog from a reputable and responsible rescue will be assessed, neutered, vaccinated, microchipped, matched to the new owner and vice versa, bringing with him a lifetime's support and an agreement that the rescue will take the dog back should the owner not be able to keep him, even if that's in 10 years time. A responsible rescue will also home check which is as much for YOUR benefit as the dog's, so they can identify and iron out any potential problems before they start and assess whether the dog you have chosen is right for your family and environment.