My recommendation would to find why MySQL tables crash in the first place and prevent them from crashing again. You can setup that cron job to run repair on all of the databases on the server for the time being. But you should find out why MySQL tables crash.
*Just don't run the cron job for MySQL repair when backups are running in progress, as it may crash your server.
If you have a managed server, contact your hosting provider and have them check your MySQL server. You may be running out of memory or your MySQL may not be properly configured/optimized.
How nay tables are crashing? I have seen some websites with specific tables ( like one storing session inf ) crashing very quickly. A possible solution is to use InnoDB for such tables and that will let you to overcome the frequent crashing. Also once we have written a script for one website, to check the website contents locally and if it detects the table error, it will auto-repair the tables. We used it until our client could switch crashing table to InnoDB.
We used check_http nagios plugin along with "-s" switch to check the string in website. That helped us to identify whether the website is crashed or now. Please contact your developer to change the table to InnoDB. Though it is fairly easy to switch, I don't want to break anything in your website without knowing the actual stuff; your developer is the best person who can do it. Yes, InnoDB doesn't support manual repairing. But it is highly recommended for frequent write tables and there is very less chance for it to get corrupted comparing to MyISAM table.
..... n who can do it. Yes, InnoDB doesn't support manual repairing. But it is highly recommended for frequent write tables and there is is very chance for it to get corrupted comparing to MyISAM table.
Nixtree you've missed an important word near "very". Is it less or high?
Well, we don't know what is causing the databases to crash. You need to find the source and to do that you first need to start with MySQL logs. Review the logs, see what you can find, run MySQL Tuner on your server, optimize MySQL, monitor the server and MySQL memory consumption, and adjust the config until you get the perfect setup.
InnoDB outperforms MyISAM under heavy load, but I haven't recommended it, so I can't tell you whether it will solve the problem or not. My first step would be to identify what is causing the MySQL database crashes before doing any work on the databases.