growing cactus for composting?

i have 2 Opuntia ellisiana cactus (both are thornless) and they grow so well the get to big and "die" then come back get to bet again and so in and so forth.

would using them for composting be a good idea, would i need to shread them to keep them from putting down roots?

if they are good to composting that would be great b/c i can plant the crap out of them and have lots of bio mass

Anything that once lived can be composted.

Composting them would be great but you should make sure any pieces with roots are completely buried so they won't regrow.  They won't grow in the dark, to my knowledge, so shredding them isn't necessary, just burying under soil or other compost ingredients. 

I would love some pads from your large-growing Opuntia. I have some but I'm not sure they are the same cultivar and I want more of them.  More cactus? Yes, please!  Maybe we can swap if I have something you might like or need.  I have lots of seeds of  native american squash, corn, beans, etc. 

i sure can send you some pads. I got 3 in diffrent locations and they do great. 2 of them do almost to good.
The oldest plant i have is planted right next to a mesquite tree. Its in it dieing stage right now as it has become so big the pads that have become stocks cant support it anymore.
the second one is planted by a patio and gets run-off from the roof. this one blooms the best. im guessing from getting more water.
and the third is in the front drive by a wood fence. (dont know what type of wood) and it does great as well. i dont really monitor it that much.
the 2nd and 3rd are both from cuttings from the first. and the first has been here sence we moved here in 97. so its had 14+ years of no problems.

how would i send them though? wrap in wet paper towel, then a platic bag then box it up??

Let's wait for cooler weather!  But yes, if I remember in October maybe you can put some in a baggie and box and send my way.  And I'll send you a lot of seeds, or something! 

Opuntia pads are pretty slimy and full of moisture.  I would just add enough carbon (wood chips, etc) to keep them from going anaerobic.  I would also shred them if you can, that would speed it up.  I am curious because I have lots of them, but I have never tried it.  Sounds like a good idea.