Outdoor Power Equipment and Small Engines - Help with Cub Cadet 2145

I am attempting to replace the ignition module on the 14hp Onan engine in my Cub 2145. I need to keep the driveshaft from turning while I attempt to take the protective cover off of the back of the engine. This cover protects the fan. In order to properly get the over off, I need to keep the driveshaft from turning. Any ideas.
Thanks

Are you sure you need to hold the drive shaft in order to get the intake boot off? For the life of me, I can't picture why you would need to hold the shaft. The boot shouldn't rotate with the shaft...does it? If you are attempting to remove the engine from the chassis so as to remove the blower shroud off the engine then why not do just this? Remove all peripheral controls, remove the drive shaft coupler screws, remove the engine mounts, disconnect the muffler and the engine should be out! Bare in mind, l've never worked on a 2145 and furthermore, (not necessarily related to anything) I didn't realize that Cub has an Onan installed in this mower. How old is it? I see, based on the parts break-down of this 2145, that it is a vertical shaft engine (as most Cubs are) and I had no idea that Onan ever powered Cubs, especially a single cylinder horizontal!!! Are you from the States or elsewhere? I might suggest using a pipe wrench to grab ahold of the shaft if you must.