Okay, we need to have a frank discussion of what is and is not a horse
Unfortunately, since the card's included in the Commander banlist, and isn't you're unlikely to experience the joy of trading a treasure for a Blightsteel Colossus - though you're allowed to run a single copy in Vintage, if you've got the cash
Also, most Prosper decks are relentless value engines that often require your opponents to team up to keep you in check, so even if your deck isnt optimized, you can expect people to keep a watchful eye
Limiting a player to only taking one more turn resolves this issue, but what if the take one more turn spell is cast one after another
toploaders: Semi rigids are popular for sending in cards to get graded but dont provide much protection, so use the rigid toploaders for regular sales, but be aware that if you use them in regular PWE (plain white envelope) sales without paying extra to mark it non-machinable, the toploader can get mangled in the automatic envelope sorters
Whether you are an experienced player or a beginner, remember that this experience involves more than just playing a game it entails channeling imagination and strategic thoughtfulness