I live out in the "country" (yet 5 minutes from city!) -- 90 acres of farmland are behind us (we don't own) and 3 acres of land in front of us. Jackson used to be off leash a lot but I always watching. At the time, my mother's dog was still here (she passed away last summer) so they would always play, stick together and never go far.
Since the other dog passed, I haven't really given Jackson the freedom that I used to. He's like 90% reliable but about 3x now, he's just decided to take off and bolt. Now... granted... there's not much he can get into... and he has always come back but we've been been working a lot harder on reliable recall w/ a 50 foot training lead. He's been doing GREAT but hasn't been off leash since the Fall. Although, the other day he got out and to my surprise, YAY, he came right back when I asked him to!
But I really wanna have a reliable off leash dog, not to let him wander near cars or busy streets, but so I know if there's a big open field, I can trust him, or if he gets loose, I'm more secure he will listen and come back.
But yes, I get nervous!