Pritam Bakshi, owner of Keen Kost newsagent on Dundas Street, fended off a knifeman with a clip-board in the latest incident, with the robber eventually fleeing empty-handed.
The attempted robbery last Friday was not the first time Mr Bakshi, who is in his late 70s, and his wife Shashi, 59, have stood up to armed thugs.
Mrs Bakshi has previously refused to hand over money to a knifeman who threatened to kill her, while Mr Bakshi has also fought off a thief despite being beaten over the head with a champagne bottle.
The couple, who are originally from New Delhi in India and have owned the store for more than 30 years, say they will never give in to "cowardly" thieves.
Mr Bakshi said today: "We're in this shop from 5:15am to 9pm nearly every day and there's no way we're going to work so hard for someone to come and take it from us."
He said the latest incident happened shortly before closing time on Friday, when a masked man entered the shop.
"He walked into the shop with a black cap on and a scarf pulled up to his nose so I knew he was up to something. He held out his arm and showed me a blade sticking out of his jacket sleeve, and told me to hand over everything in the till. I said to him, 'You must be joking.'
"I knew there was enough space between me and the other end of the counter to dodge his knife so I took a step back, grabbed a clipboard for protection and shouted for my wife down in the cellar.
"I think the thought of having to face both of us made him lose his nerve so he ran away. I chased him outside but he disappeared.
"These people are basically cowards. They lose their nerve the minute someone stands up to them."
Mrs Bakshi, who has six children with her husband aged between ten and 25, fought off her own assailant around a year ago, when a man entered the store and threatened her with a knife.
She said: "It was a similar situation to Friday. A man walked in, handed me two bags and demanded all the money in the till.
"He threatened to kill me unless I did as he said, but I removed the keys to the till and threw them down to my son in the cellar.
"I shouted to my son to come upstairs and the man ran away."
The couple said the most serious incident happened around eight years ago when Mr Bakshi had to physically restrain an attacker to protect himself from being repeatedly beaten with a champagne bottle.
Mr Bakshi said: "On that occasion the man whacked me over the head with the bottle.
"He said he would hit me again if I didn't hand over the money in the till, but I reached up and grabbed both of his arms and forced him back.
"He had hit me pretty hard and the blood was streaming down my face and into my eyes, but I wasn't going to let him go.
"I had to go to the hospital and the nurses said I had lost so much blood that they were amazed I didn't faint."
Police are appealing for witnesses to the latest incident, which happened around 8:50pm on Friday. The suspect is described as white, 6ft with a local accent. He was wearing a black jacket, black trousers, a black hat and had a black scarf covering his face.