Hi Julie,
Sounds to me like your Shar Pei may be suffering from separation anxiety, I have a two year old Shar Pei and she too suffers from it only she does not defecate she chews things when we're out. Does this tend to happen only when you leave them ie go to work or bed? if so then sounds like an almost definate case of SA, try changing your routine this is somehing that dogs are experts at picking up on they know exactly what is going to happen next by your movements.
Secondly, dont make a huge fuss of leaving them, keep all the attention really low key for about 20 mins before you go to bed, minimal talking and minimal eye contact do the same in the morning. If they jump up then dont look at them and just say "down" but with a gentle stroke so there is still a minimal amount of affection. once they have calmed down or as I said after 20 mins or so then go to them and pay them some attention. This also helps to assert your Dominance over them, dominant dogs will act non chalont when being demaned attention from and will go to the other members of the pack and demand attention when they want it.
Another point here is that shouting will do nothing but teach your dog fear! Dominant dogs never bark loudly or go crazy or nuerotic they simply give a low rumbling growl to let lower members know they're boss. if you catch your dogs doing something wrong then by all means correct the behaviour with a low toned rumbling "NO" and a gentle but assertive touch to the shoulder.
Something else you could try is a Dog Appeasing Pheremone Diffuser (DAP) you can get them from the internet or your vets (although internet tends to be cheaper) and all it is a plug in like an air freshner that gives off a pheremone which a *** produces after having pups, this helps to calm and reassure the new puppies. It works in exactly the same way for adult dogs! they cost about £17 and tend to last over a month. you switch them on just before you go to bed and turn them off when the dogs are in your presence. And dont worry we cannot smell it only the dogs can so it wont give off any funny smells in your kitchen!
You can also try some fun obedience training about an hour or so before bed to make sure they have tired minds, walks are great but they may not necessarily provide sufficient mental activity.
Sorry for the essay but I hope some of this helps!
Caz