Hi Mehmet,
The iBGP will not provide an isolation between the two ISPs, and you will need to perform filtering to prevent routes form one ISP leaking to another.
In the case you have presented, it is still necessary to make sure that you advertise only your own networks to the ISPs. The tools suggested in the article you have mentioned are perfectly valid and usable even in this case - you may use whatever filtering tools when advertising routes to your ISPs, provided that these tools can precisely distinguish own local networks. One of the easiest ways to accomplish this is to filter routes based on their AS_PATH attribute - advertise only those paths to ISPs whose AS_PATH is empty, i.e. matches the ^$ regular expression. This approach is also explained in the article.
Please feel welcome to ask further!
Best regards,
Peter
