I don't understand the problem with database links. You have two schemes and different users. You can make a database link and give synonyms for tables in the linked database. And finally you can grant or revoke access to tables in the database and the linked database for every user.
Thanx for this info. I'm not much familiar with database links because this is the 1st time I've even considered to use them in an application. I'll discuss this with my employer and see if there are any other causes why he wants me not to use it.