> it's hard to keep the integrity of the database when
> some users openning Excel or others DB engines to
> update some records. How can I do to protect my .dbf tables ?

You meant to stop users from updating those tables
over a network? Give read-only access to them via
the user privileges of the network OS.

If you were talking about sharing access to the tables
with Excel or other DB engines, can't flock() or
exclusive open solve your problems? I supposed those
Excel and DB engines use dBase method of opening
dBase tables. If not, load SHARE may help.