Steve,
Diff cover braces are one way of protecting diff covers. Replacing the cover with one more suited to a high performance environment is the other.
This is a pic of the damage you can sustain with a stock 8.8 OEM Ford cover and also a Steeda brace for the cover to prevent the damage;
The Steeda brace attempts to take the force that destroys the cover, route it through their brace and deliver it to the main differential housing through the periphery of the cover and the cover bolts.
This is a pic of a billet cover built before Ford offered their upgraded rear cover. These are pricey, difficult to find and essentially indestructible.
This is a pic of Ford's current
performance rear cover for the 8.8 IRS, M-4033-G3. It is well thought out, designed and available through Ford Racing Performance Parts (FRPP) as a stocking part.
While lacking some of the bling and brute strength of the billet cover it is none-the-less a very good solution to the tender OEM rear cover design. Not that it can not be broken but I have yet to hear of one breaking.
Ed
p.s. it is not HP that breaks diff covers it is torque, hooked up and accelerating the car combined with a poorly hung IRS center section that allows center section movement under acceleration.