If running around the park is to easy for you, try the ParaJogger.
Its a miniture parachute that you attach to your back.
The faster you run, the more resistance you get. This function much like weights during weight lifting.
The resistance is also adjustable by a single rope to the middle,
which controls how much air is allowed to escape. The hole is also there to reduce oscillation of the parachute by allowing some air to vent, preventing it from smacking other joggers.
To ensure that the parachute will remain open when the jogger is stationary, the chute is is lined with the same material that keeps popup tents stiff.
This all leads to being able to exercise better in a smaller park.
... You will look stupid tho