His first job in 1943 was with the federal Department of Agriculture as livestock fieldman. This put him in contact with the livestock auctioning business and he met J.W. Durno, top livestock auctioneer in Western Canada at that time. Durno was in the twilight of his career and Jock saw an opportunity for a young auctioneer with a good knowledge of purebred pedigrees.

Following the course at the Reisch American School of Auctioneering in March, 1949, he tried selling at a few sales. He was encouraged enough that he quit his job in 1950 and started Blacklock Auction Service. He also became secretary of the Saskatchewan Hereford Association.

Jock quickly established himself as a knowledgeable livestock auctioneer. He learned the pedigree of every animal he was to sell and was able to relate that to the performance of the animalís forebears and siblings. This was valuable to breeders in deciding whether those genetic factors would upgrade their livestock. Early in his career the emphasis was on show ring successes, but later Jock also provided performance test results in selling purebred animals. Farmers consulted him about the suitability of introducing certain blood lines into their herds.

His knowledge, his humor and his sales management capabilities moved him into prominence. Soon he was selling at major events such as the Calgary Bull Sale, the Regina Bull Sale and production sales of leading pure-bred breeders. In 1980 he sold 14 of the top 20 private sales in Canada. He sold all of the major cattle breeds but was particularly in demand for Hereford sales. He also sold swine, sheep and at farm auctions. He set new records for dollar returns in many of these sales. His two brothers, Ben and Bill, worked with him in selling and, later, Jockís two sons, John and Bob, learned the trade and took over when he retired.

In 1961, in partnership with his wife, Mabel, he opened an auction mart in Saskatoon to provide a model sale facility for farmers.

Jock served for many decades as director of Saskatoon Industrial Exhibition and in 1967-68 was president. He served a term as reeve of the Rural Municipality of Corman Park. He was a member of the Board of Governors of the University of Saskatchewan.

He was named a member of the Canadian Hereford Association Honor Roll and was awarded a scroll from the Saskatchewan Livestock Association for service to the livestock industry. In 1994 the Saskatchewan Auctioneers Association gave him a place of honor in the Auction Era display at the Western Development Museum in North Battleford.