  We present several models to describe the stochastic evolution of stocks that
show some strong resistance at some level and generalize to this situation the
evolution based upon geometric Brownian motion. If volatility and drift are
related in a certain way we show that our model can be integrated in an exact
way. The related problem of how to prize general securities that pay dividends
at a continuous rate and earn a terminal payoff at maturity is solved via the
martingale probability approach.
