If you have a property under contract, nobody can circumvent you or steal your deal, the only way that could happen is if your contract expires in which case, you no longer have any control over the deal. If it is actually a deal, then you should have no problem selling it to any number of your vetted all cash buyers (you need to have buyers in place first before you go locking deals). Others will argue against that advice claiming once you find a good deal, buyers are easy to get, however, there is down side doing it that way and no legit downside doing it with buyers in advance. With having vetted buyers, you should know their criteria and as such, search for properties that meet those criteria, that places you in a much stronger negotiating position with potential sellers when you know you have a buyer or multiple buyers that will fit in this box. Additionally, and probably most importantly, if you don't have vetted buyers in advance and you market the property on FB or other online or direct sources, you are marketing a property without a license which is against the law in just about every state if not all by now. You must have a real estate license to publicly market a property you do not own title to. Also don't listen to those who will tell you that you are marketing a contract and not a property either, that is simply not true and in a court of law, good luck arguing that.
To properly and legally wholesale, you need to know your market, build a qualified and vetted all cash buyers list, build a marketing plan to attract and receive qualified seller leads, and know how to negotiate and properly contract the deal. Without a license, you are not permitted to publically market the property so you either need to get a license, close on the deal with cash or borrowed funds and resale right after (double close), or properly set it up with a set buyer in place. The last of these options has several options. If you are searching for one or two specific buyers, you can prearrange to make offers in a new entity or trust and name the buyer as a member/owner of the entity (or trustee or beneficiary of a trust). Then at closing and in escrow, you simply have that buyer pay you your fee in escrow for the rights to buy you out of the entity or trust. No public marketing to violate the laws, no worry about locating the buyer before your contract expires, etc.
I have posted many times on BP how to properly structure wholesale deals, try and search to find them or search through my specific posts (although they are over 15k).