A lot of individuals with colostomies have trouble getting their bags to stick properly, or more often, getting the bags to keep sticking. However, knowing that adhesive problems with colostomy bags are common doesn't necessarily make it any easier to deal with. There are a few easy things you can do to help the situation, though.
If you are consistently having adhesive problems with your bags, consider changing the bag more often as moisture can build up on the skin and cause adhesives to stop working. Alternatively, try another brand of bag or try bags that belt on, rather than those with the sticky backs.
Also, consider the time when you are changing bags. For example, if you are changing bags right after eating, your abdominal area may be stretched and so the bag won't adhere to the skin as well. If you are replacing bags after a shower or bath, the area may not have fully dried--try towel drying it and then using a hair dryer on a low setting to ensure the skin is completely dry before putting on the bag.
Adhesive problems could also be due to an improper fit around the stoma--if the hole is too large, fluids can leak out around the stoma area. However, if the hole is too small it will put pressure on and potentially injure the stoma so avoid this as well. If you are a more active person, it could be that your colostomy bag is moving around too much for the adhesive to hold properly. Consider wearing a colostomy belt to help hold the bag in place.
If you're looking for a more temporary fix to get the bag sticking for just a day, consider using bandage tape to tape the sides of the sticky pad down. You can also apply a bit more stomahesive paste to the larger area of where the pad will stick instead of only right around the stoma to even the surface out and give the pad a bit more sticking power.