NO BIKES IN THE SKATEPARK!
it is tough to mix the two
the bicycle and skateboard move at different speeds and take slightly different lines
then there is also the notion that bicycles cause damage to the skate terrain with their bolts and pegs
so... if the bicycle is not allowed in the skate park... give the bikers a place to ride their bikes!
PUMP TRACKS and SKILLS PARKS are great Urban-Suburban Answers to this dilemma