Issue with revoking privileges from public

 Hi Gurus,
Please help me here:

I want to revoke the following privileges from public:

revoke execute on dbms_job from public;
revoke execute on dbms_lob from public;

But some of our application users may be using these through public access. So revoking the privileges may affect these application users.

How can i find out whether any application user is using these objects or what ?

Thanks in advance
Anoj