I want to let my cat to the garden but I don't want her to escape. I have a 6 foot tall fence and there's also a brick wall garage with a flat roof. Do you think that's enough or I should put something like an electric fence? Although honestly the only thought about it freaks me out. Please advice!
First off, don't use an electric fence for cats (or dogs). If they get scared, they can run into the fence and get tangled in it.

My cats have always been indoor and outdoor, and they always come back to the house when they leave. Cats like to defend their territory, and they come back to the yard and house to do so. They also know that they get love and food in the house, so they'll come back for that too! That doesn't mean that all cats do this, but most I've seen do.

She probably will jump on top of the wall if you let her out, but that's because cats like to be up high so they can survey their surroundings. If she DOES leave, you could go get her and bring her back. If you do this a few times she might get the idea.

Another option is to sit by the door and watch her to see how she acts and if she tries to leave, you can get her.
teach it to come wen you call.
boyquail If she DOES leave, you could go get her and bring her back.
I would panic if I saw Miky leave to be honest! The only thought that he can escape if he's allowed to go out and that I may never find him is too scary for me. Emotion: tongue tied That's why he is indoors. I'm amazed at your calmness when you speak about bringing a cat back so easily!

Anon make sure there are no gaps at the ground in your fence... cats will sometimes dig their way out!
I forgot to say in that part that one should watch the cat from afar! That's why I was calm about it. You'd see that the cat left, so it would be easy to get him/her back.

I've had indoor cats escape, it IS scary. But we've always found them.
Well that's better but I can't get rid of the fear that even if I watch my cat and see him leave he can easily get frightened by something as soon as he's escaped, for example by a dog or a passing car, and then he can just run away leaving me no chance to follow him. Oh well... I'm too fearful for this stuff. Emotion: smile
My neighbors put their cats on a long leash hooked to the ground. The cats seem pretty content.
Yes, the cats can be easily trained to a leash or chain run, like a lot of dogs. The only thing to remember is to use a well-fitted harness instead of a collar, because cats can slip collars. If the harness gets hung on something, it doesn't choke the cat because the weight is more distributed (still is uncomfortable, though!). We've leash/stake trained two of our three cats (the other is terrified of going out the door). The other option is to buy those outdoor cat tunnel things.
Both our cats easily scale 6 foot fences. They make special things you can mount onto the top of fences to keep cats in; most have netting that angles in so the cats can't scale.