Given that the solutions to the cryptic clues are as follows...
A vessel with no obtuse ends! = CANOE = CAN + (n)O + (obtus)E &lit!
To give the greatest expression of pain = BESTOW = BEST + OW
This man, one who provides citations in the wrong way (a liar, primarily) is against common beliefs = HERETICAL = HE + CITER< + A + L(iar)
Mad genius eats ball of fire = IGNEOUS = GENIUS* around O ('ball')
Mark, in good shape, goes back, gets a drug = DENOTE = TONED< + E ('drug') (solved by @jafe in comments)
Gasp! That guy, placed at the top of the hall of fame? = PANTHEON = PANT + HE + ON (solved by @jafe in comments)
Got there roughly at the same time = TOGETHER = GOTTHERE*
Blazing row that shows escalation = GROWTH = _G ROW TH_*
Dry, dishevelled owlet = TOWEL = OWLET*
Reflection of a lake captured in fine instrument = THEREMIN = MERE< in THIN
Modern unit of weight = NEWTON = NEW + TON &lit!
The beer talks random nonsense = BLETHERSKATE = THEBEERTALKS*
...we next notice that these answers can be split into three groups...
...depending on whether they contain a run of letters which is an anagram of the numbers ONE, TWO or THREE:
ONE: CANOE, IGNEOUS, DENOTE, PANTHEON;
TWO: BESTOW, NEWTON, GROWTH, TOWEL;
THREE: THEREMIN, TOGETHER, BLETHERSKATE, HERETICAL.
Next, we should notice the numbers in the corner of each box that contains a clue:
If we treat these as indices and look up the letter in that position within the word, we can read 'A SLITHERLINK'. This implies to me that we now need to solve a slitherlink grid-deduction puzzle based on whether each answer contains a 1, 2 or 3.
Our initial slitherlink grid and its final resolved state then look like this:
And superimposing this on the original connecting wall yields this:
Finally, as pointed out by @HTM in comments (nice spot), let's focus on the cells containing the 'holes', and specifically...
...the shape of the loop that passes around their cell borders:
We have here an implementation of the pigpen cipher! If we order the cells by their Roman numerals (and include the cells' central dots) we see this sequence:
This is the pigpen encoding for LOOP, which means that these holes are LOOPHOLES! What an incredibly apt name for them, considering they are formed by the slitherlink loop. Great puzzle!