The way to stop them exploding is to NOT EVER and NEVER (I hope I've made the point there
) allow the cooking water to exceed 80C.
The idea is to poach them and not boil them so if you see rapid bubbles rising through your cooking water then it's too hot.
Get a good thermometer and monitor the temperature carefully.
Poaching time at 80C should be around 45 mins for hog casings (the way to work it out is to masure the width of the pudding in mm and add 10%. i.e. if the width of the pudding is 30mm then 30 + 10% = 33 so you would poach them for 33 mins at 80C.
On the subject of pricking, don't do it as you let flavours out and water in. You won't need to prick them at all if you follow the instructions above.
This is how they are done commercially.
Good Luck.