If you aren't using the timers in 89c51 itself, you can use one to simulate your own watchdog timer. It is very easy.

In fact even if they are both used and at least one of them is used to generate a constant delay, you can simply use it as watchdog timer by adding a few lines in the interrupt subroutine.

I had described a simple program in an earlier thread...you'll just have to search for it.

Kundi