It obviously changed over time, but after about 1967 it became a very robust boundary. A typical section of the border was two fences (made of nearly unclimbable expanded metal topped with electrified barbed wire that served as a sensor) separated by a wide open space in the middle with armed guard towers overlooking. The intervening space often contained ditches and mines, but it wasn't as though you were guaranteed to set off a mine if you traversed the border on foot. Additionally, a 5km wide zone around the border was heavily restricted with all roads monitored and locked down.

Crossing the border in 1973 wasn't impossible, but was a herculean task. Fortunately, it was just prior to the 1974 "order to fire" by Honecker which gave guards nearly carte blanche to open fire on suspected escapees in the border zone, but it's not likely that made a huge differences in actual chances of surviving an illicit border crossing.

That said, it wasn't impossible, and many tried. Your best bet was probably to trek in on foot, find an unmined zone, and be well prepared. In the 1970s over 5,000 people tried to make their way across the border, most were arrested, a few hundred were killed (by landmines, by mines at the fence, by border guards), and something like 200 actually made it across. So your fictionalized portrayal is somewhat realistic, but does point towards it being a rather harrowing adventure with a low probability of success.