Tomcat JNDI Question

[Tim Terry]

I currently use tomcat in a multiuser environment where each user has
their own virtual host. I would like to enable JNDI access for the
users. I understand that the default servlet context can be used to
define JNDI resources specific to a virtual host. How will i prevent
users deploying applications to their virtual host with resources that
use the same JNDI name as another application on a different virtual
host? As i don't want users over writing other user's JNDI resources or
accessing them. Are JNDI resources specified by an application in one
virtual host accessible from another virtual host? Each user currently
has their own role, if that helps matters.

Thanks in advance,

Tim