He was most known for his work in cave photography, laboratory rope testing, especially in connection to knots, and his contribution to the development of the single-rope technique.

[4][2] Despite Planina's achievements in botany, his herbarium was widely known,[3] he decided not to pursue an academic career but took a job in the Development and Technology Center of the Iskra electronics and automation company where he specialized in the area of biologically and air-pollution based corrosion of electrical contacts.

He worked in various capacities, including the post of research project leader and this field remained his occupation all his professional life.

[18] In the mid-1960s there was a change of generations at Ljubljana Cave Exploration Society, pre-WWII team gave way to younger cavers.

The greatest impact had the 20-member expedition in 1969 to the cave Žankana jama (as it is called by the locals) near the village Rašpor, in Istria, Croatia.

[22][23] It is a sinkhole of a local creek that dries up in the summer, after some initial smaller shafts a large, 200 m deep inner abyss opens up.

[19] The next big expedition, led by Planina, was to Brezno pri gamsovi glavici [Abyss at the chamois head] above Lake Bohinj in September 1972.

Outside Slovenia, he was well acquainted with Velebit mountain ridge in Croatia and Durmitor massif in Montenegro – some parts of both botanically and speleologically rich areas he knew better than the locals.

[5][3] In the 1970s, when the single-rope technique replaced the use of wire ladders and both simplified and facilitated the mastering of deep shafts, Planina got interested in the issue of safety.

Proper lighting of large underground spaces, especially with low-reflection surfaces, such as mud, requires a sequence of multiple flashes at full power, usually from several positions.

Planina was a bridge between generations and a great mentor, he will be remembered for his problem-solving ideas, sense of humor, and extraordinary zest for caving.