Nieve owner- needs advice!

Hi everyone! Most of you know I have Calvin. He is almost 1 year old now and the best dog ever! My question is this....I see people walking around parks with their dogs walking nicely next to them OFF LEASH and I am wondering how they train that. I would like to have Calvin hang out with us in the front yard, but have never actually had him off leash for fear of him running off. He did respond to the "come" command MOST of the time, but it has been about 5 months since we have used it due to "The Lizzie Factor". How do I train him to hang out with us off leash without actually letting him off leash? My other concern is that if I "try it out" in the front yard, I'm afraid he may remember his 3 day adventure with Lizzie and start to go on another one! Does that make sense? Help!
Thanks! Leslie