Love it mate, gave me a laugh after a few brews tonight!!
Few tips mate for when using the "bulldog". Get yourself some inch nails. These are your best friend when you unleash the dog. The mini relies on the gripper being anchored properly. Normal 3/4 nails should hold the gripper in place, but if the dog starts lifting the gripper, place inch nails in between the nails already in place. If the concrete is hard as, and you cant get a nail in, drill and plug is the next step, as you have found out. Another way is to double up the smoothedge. Place another row of s/e in front of the row already down and cut back the underlay. If the floor is a real bugger you could also use liquid nails to secure the s/e.
A tubed power stretcher would probably be the ideal tool to use, but ill let MarkS give you tips on using one of those.
When using the dog, i have found taking a few bites at a time gives the best result. Going for the big bite to start with will usually rip the s/e. Especially in re stretches, small bites are the way to go so you don't rip the carpet. Also take your first bite in the middle of the wall your stretching on, and knee kick about a foot on a slight angle in each direction, than move the dog as required.
And this may sound trivial but make sure the dogs teeth are clean when using it. Yarn in the teeth can lead to the dog slipping on the carpet, and if its a nice wool carpet it can leave a nice rub mark on the carpet.
Had a laugh about pricking yourself on the smoothedge. you probably know why it stings for so long after you prick yourself, but for those that don't, its because most smoothedge is treated with formaldehyde to prevent mill due and termites. Tiniest pin prick can sting like a real bugger!!
Glad you sorted this out mate, sounds like you had fun!!
On a side note Im laying a new type of carpet on Monday, Velcro backed, there is talk of a velcro smoothedge and velcro tape for the joins. "way of the future" i have been told. Sounds interesting. Ill update when i get a chance.