For all practical purposes, this is a ten-year-old who has never been fully toilet trained. To adopt a wait-and-see approach may be well intentioned, but it is irresponsible. This is a medical problem that needs attention, beginning with a full medical evaluation to determine if all is well from a structural point of view (it likely is OK). The problem of impacted bowels can be a recurring problem if it is not dealt with in a systematic, comprehensive manner under medical guidance. This will work out OK, but the situation needs to be addressed in an active manner. Passively continuing down the current road will only bring more of the same.
I agree that definitely at 10 yrs old, he should be using the bathroom regularly. I would advise getting a second opinion on the medical side of this...make sure his body is working properly.
Have you asked him straight out why he prefers to poop in his pants instead of the potty? It could be that he holds it at school because he doesn't want to be embarrassed, yet at home it's always been OK to go in his pants, or diaper. Your husband thinks it will fix itself over time but if that were true, he would have been using the potty long ago. I think your husband is enabling him and never guided him into using the potty on a regular basis. Your 10yr old has been doing this for a LONG time and it may be hard for him to change, even though he may very well want to make that transition.
Personally I wouldn't have him on laxatives or meds on a regular basis...it may make it harder for him to hold it, ya know? I know if I take a laxative, I may not make it to the toilet either. Talk to him. Be upfront and direct, he's old enough for your honesty now. Discuss how he feels about it, ya know. He might be waiting for someone to take the upper hand on this situation.
Barring any physical/medical problems,...maybe you can approach this the way you would with a toddler...
*Make him go at specific intervals during the day, even if he says he doesn't have to go...he still has to sit on the toilet for a time. For example, every 2hrs or so it's potty time.
*You could start making him be a part of the clean up. Most people don't want to be dealing with poo so if he has to clean it up, maybe he won't make the mess.
*Employ the "your friends all use the bathroom" tactic. It's up to you if you think this "peer pressure" will work.
*Maybe even get him a toddler potty he can keep in his room or in a specific spot so he can have easy access to a potty. Just like with toddlers. My 2 yr old is using her potty all the time for poops and I found that it really started when I gave her her own potty. We actually take it with us everywhere. (The Baby Bjorn Little Potty) You never know when a big potty is not accessible, but the little potty is always in reach.
* I would also practice EC - Elimination communication. This is what worked for my daughter. It's a natural, no pressure approach to learning to use the potty. Obviously, this is geared towards infants and toddlers, ages birth to 3-4yrs old. But I believe it would be helpful for your 10yr old as well. Check out the book - "Diaper-Free Baby" and the following websites:
www.diaperfreebaby.org
www.natural-wisdom.com
http://en.wikipedia.org/wiki/Elimination_communication
There are yahoo groups and forums for EC and EC Late Starters....
Take an active approach to this problem, don't wait for it to "fix itself". He's been doing this for 10yrs....don't waitfor another 10yrs to go by before you really do something about it. the longer you wait, I believe, the harder it will be 'cuz he'll have been doing oit for SO long.
Good luck, I hope all goes well for you both.