To stay alive in spikes, create a new skate park that has spikes in it. Then try the park and grind the edge of the spike hole. It doesn't matter what kind of grind it is. Then lean into the hole and you will fall into the spikes but get up and you can skate in the spikes. This cheat is great when playing tag in two player mode. (Just Don't Tell The Opponent The Cheat!!)

P.S.- May Not Work All The Time But Works About 90% Of The Time.