DSM Tower Controller reported a runway incursion and stated there has been an increase of runway incursions at DSM airport.

Narrative

I was working CD/FD (Clearance Delivery/Flight Data) position in the Tower; and was occasionally monitoring LC (Local Control); which was combined with GC (Ground Control) at the time of the event. Aircraft X landed Runway 13 and turned off at [Taxiway] D4; to taxi to the south hangars. Aircraft X was instructed by LC to taxi on D; and hold short Runway 23; then instructed to cross [Runway] 23; and hold short Runway 31 at [Taxiway] P. Aircraft Y landed behind Aircraft X; when LC noticed Aircraft X cross the hold short line for Runway 31 on Runway 23. LC told Aircraft X to stop; and I scanned northwest to see where Aircraft Y was in relation to the runway intersection. Aircraft Y appeared to be at taxi speed and slowing; and was instructed to exit Runway 13 at [Taxiway] D4. Aircraft Z was observed executing a pilot initiated go around. LC instructed Aircraft Z to enter right closed traffic for Runway 13; and did not overfly Aircraft Y exiting at [Taxiway] D4. The runway intersection area at DSM has seen an increase of runway incursions; by both experienced pilots; and student pilots. Through Controller vigilance and scanning; we have made extra efforts to concentrate on this hot spot area of the airport. Even though construction has limited many of the routes available to pilots to taxi on the surface; issues still persist; even with correct readbacks from pilots. Controllers try to give simple instructions to pilots and use positive control by not introducing additional risk to a situation. Pilot/CFI outreach and education from the FAA could help get pilots better perspective of a Controller's responsibility; and what is expected of pilots.