How to stop falling bicycle chain?

Virtually every time I go in my bike chain is soiled or fall, usually when change gears, but sometimes you just randomly it seems. Its been like this for two years and when we took him to the bicycle repair shop that said there was no nothing wrong, but when I sat on the chain again continued doing the same as described above. I have a couple of bikes around which laying have doubled in the frames, besides my bike, do you think there is any home repairs that might try? Any input is appreciated, thanks

if you can take your wheel carfully taking it back and inspect the grovves between the gear teeth check to see if there are nicks or worn these sections can add to its chain or to jump next check to see if you have the setting on your ab derailer is a little screw that Farrel to ring in the chain derailer and push the box near of derailer even more the suspension to get it out, so it is a few millimeters from the top of the gears of the cage and the ring of the chain in lower gear it will help tighten the chain and then by changing gears and when you reach the top and bottom gear to see if the chain tries to jump when you press the shift lever back to the cut point or when you sit in speed if there is a barrel nut on the shifter and the shift to the bar hadle if it is expected to jump this helps

Bike Chain Bottle Opener $10.00 These bottle openers are ingeniously green. They’re made from recycled parts of the millions of bicycles thrown away each year. Perfect for poppin’ and good for the soul….

Park Tool Wall Mount Bottle Opener $16.26 Park Beverage EssentialsCleverly disguised as a water bottle cage, the BO-5 attaches to any wall, workbench or cabinet and includes a handy water bottle style cap catcher…

Resource Revival Recycled Bike Chain Bottle Opener $28.50 So fun to play with you’ll wish twist-offs had never been invented. Flexible recycled bike chain handle and a colorful anodized aluminum head….

Stone Cold [VHS] $9.98 Stone Cold…

Chainsmoke (Mountain Bike) [VHS] $9.95 Shot entirely on 16mm film, Chainsmoke is packed with racing, freeriding, interviews, crashes, and an awesome soundtrack. Featuring shaun Palmer, Tinker Juarez, Alison Sydor, Myles Rockwell, Missy Giove, and many others! This film will make you want to ride! …

Bike Chain Necklace $12.5 This necklace features a bike chain.

Bike Chain Link Gold Hip Hop Bracelet #22 $49.95 Bike Chain Link Gold Hip Hop Bracelet #22

Black Bike Link Chain Bling Bling Hip Hop Bracelet $69 Black Bike Link Chain Bling Bling Hip Hop Bracelet

Weaver Covered Bike Chain Hackamore $30.95 Weaver® Gum Rubber Covered Bike Chain Hackamore is a mechanical hackamore that’s good for horses with bitting issues or who have had trauma to their mouth. Available in horse or pony size. With it’s covered bike chain noseband this hackamore offers good control and is popular with barrel racers and ropers. Gum Rubber Hackamore Features: Stainless steel   Gum rubber covered bike chain noseband 7-1/2" cheeks for ponies or 8-1/2" cheeks for horses NOTE: This hackamore does not come with a curb chain.