Why would you want to "monitor" a student on a solo navex? The whole point of the exercise is to let the student gain confidence without anyone looking over their shoulder. Before you authorise the flight you make sure they are competent, then you let them go. Wherever they go, or whatever they do is largely irrelevant, they will learn from the process. If the students think they are are being monitored, they will perform for the monitor and the value is lost.