pit bulls
cars
bicycles
dust or pollen
dogs on leashes
garbage trucks
thunder storms
chemicals in the air
modern running shoes
raised edges on sidewalks
unforeseen bumps on roads
gopher holes
being kicked off tracks
bees on grass running barefoot
tracks locked up behind 8 foot tall fences
no more dirt tracks or dirt roads to run on
people walking two or three abreast on tracks
being kicked off sidewalks by people walking dogs