That is a tough surgery, i have worked with quite a few vets over the years & very few i have known or known of was able to perform the surgery perfect most of the time. Only because of one little itty bitty miss-hap will take away all your dogs control over his bowels.
Any good vet will tell you this is a last resort. Have you gotten a second opinion? Have you tried different foods & additives/supplements? The higher the fiber the more poops but the less likely to have anal gland problems.
Does your vet always just extract them or have they infused them before?

If you find a reputable vet that specialises in this field & you have tried other resorts I think you will have no problem with the surgery