Welcome to the forum, OrangeEyebrows!
You're not the only one who has puzzled over those blasted hurdles--which are described on page 50 of the HC hardback as "wood licker wood wicker hurdles". There is even a google entry which only leads you to the page of text. Knowing HC penchant for typographical mistakes (and since I don't know if the Transworld edition says anything different), I suspect that the "wood licker" part of this is a printers error. Wicker wood hurdles, on the other hand have a long and varied history and are still very much in use (and available for purchase) today.
The more important passage is, of course, the one before Sam burns them. When he asks the barman "how important" they are, and is told they're just used during the annual sheep's fair, and are stacked up so as not to be in the way. But, for some reason they are also regarded as something of a landmark.
In my judgement, the placement of these passages regarding the burning of the hurdles and Sybil's concert, which are interwoven, makes it quite clear that these hurdles have been used as some time in connection with the goblins. While Sybil is changing the world by awakening the awareness & conscience of the movers & shakers of Ankh-Morpork, Sam is laying down the rules for the locals. I doubt they'd have been much impressed by a harp concert. But Sam's huge bonfire, combined with his his explanation that the magistrates are being brought in for questioning, that the rule of law is to be followed, and specifically, Sam's explanation and warning that the goblins are now under his protection and the protection of the law. And, that means that the law is something that applies to everyone--rich & poor, human & goblin.
But as Vetinari says when he lectures Vimes--law cannot be applied retroactively ( no matter how wrong an action may be ) and therefore, the killing of the goblin wife was a slaughter not a murder. But things are changing thanks to the concert that Sybil has arranged. The song that Tears of the Mushroom played has caused the nations of Discworld to adopt what they call "the common law" (p.390) recognizing that goblins are sapient beings, and thus entitled to the same rights and protections as humans, dwarfs, trolls, etc.. But as Vetinari acknowledges, Sybil has far outstripped his own efforts to get something accomplished. Vetinari tells him that he (Vimes) will be remembered for this weeks work, even if the most important part was done by Sybil.
