I have used acrylic fortifier/bonding agent. It surely makes it stronger but not sure if that makes it resistant to cracks. People say they have used elmers glue as a substitute but I have not used it yet. I have also used fibers but they are a bit of a pain. They tend to clump together and you have to make sure they are evenly distributed.

Since I sift pine bark for my soil mixes I use the very fine pine bark (that goes through 1/8 mesh) as a substitute for peat. I have no idea if that makes it any stronger or weaker. So far I have stuck with 1:1:1 of cement/pine/perlite and none of my few pieces I have done so far have cracked. I think the key is cure them properly.

..... "I know sometimes cement sections in most big box stores have additives, has anyone used, or have good reasons to use these in hypertufa, I mean proven past results in stronger pots, statues, etc"

I have used both fibers and ad mix fortifier. I honestly cannot tell if my containers are stronger. They have held up for many years with those two included. I only use ad mix on larger pots or cement leaves ( cement leaves tend to be thinner - Portland and sand only) As I have said in the past, if you cure the piece correctly you will have the best chance at making a stronger project.

Hmm, I've never thought of using wood fibers. I usually use peat moss. My local Lowes doesn't have any fibers, like fiberglass to add unless you cut up insulation or something like that, which I won't be trying. I may try the liquid stuff sold in big box stores. I wish I could find a recipe for the Elmer's glue version. By "liquid stuff" I mean polymers. I have made pieces that have cracked before, so my curing must've been bad, or not long enough. They were kinda thick though. I want to make a trough of medium size, maybe 16 inches by 25 inches and at least 8 inches deep. This is approximate size. I know that I would likely make a block those demensions and carve out the insides after it sets up. So what would you do different?

I want to make a trough of medium size, maybe 16 inches by 25 inches and at least 8 inches deep.

Find a large Styrofoam cooler about the size you want. Use this for the outer mold. Then find a cardboard box slightly smaller that the cooler, If you cannot find the right size box you can cut 4 panels ( or inner walls) from Styrofoam building insulation ( comes in 4x8 sheets, use maybe 1 " thick) Then cut 4 inner walls. Use duct tape to hold the walls together.

I do not have a photo on making this, but just google Hypertufa inner and outer mold . There are lots of similar molds using cardboard boxes ( not my favorite) and eventually you will see an example with Styrofoam.