I see a potential food safety problem. Keeping the marinade is NOT suggested in any of the literature I have on the subject, information from classes I've taken, or in any of the information I received when I was certified to teach dehydrating classes. Nor is it suggested in the USDA information sheet I've linked below. Therefore, I would suggest you not reuse it.

BUT, if it's something you decide to do anyway, these are some precautions that you could take to help destroy bacteria. Make sure you heat the leftover marinade to a boil to kill bacteria from the raw meat juice after you remove the meat from it. Cool the marinade quickly in an ice water bath and promptly freeze it. When you use it again, thaw it in the refrigerator or a quick zap in the microwave - not room temperature - and bring it and the meat in it to a full boil so the meat is heated to 160-degrees F. prior to marination, and marinate it in a refrigerator that maintains a temperature of 40-degrees or colder.

Meat and poultry jerky must be heated to 160-degrees F to destroy microorganisms when you make jerky and you can do it using one of these two methods.

-If the meat is marinated, heat the meat in the marinade prior to drying by bring it to a boil to assure the meat heats to 160-degrees F.

-The second method is to heat the jerky in a 275-degree F oven for 10 minutes AFTER the dehydration process. [I use this method when I make ground meat jerky (I usually use ground bison because it's so lean), which uses a dry seasoning mix in the lean ground meat and extruded through a jerky maker.]

-Grainlady

Here is a link that might be useful: Jerkey and Food Safety

The other approach is to make up just enough marinade for the amount of beef you're making in to jerky. This is my basic jerky recipe, from which you can make all sorts of variations; this amount of marinade is sufficient for about 5 to 6 pounds of beef, which I find fill my Nesco dehydrator's eight trays fairly full. And there's only an ounce or two of marinade left over once I'm done.

Guinness Beef Jerky Marinade

5 to 6 lbs lean beef, sliced thinly--see Note 1
2 bottles (12-14 oz each) Guinness Stout
2 tablespoons kosher salt OR 3 to 4 tablespoons soy sauce--see Note 2
2 tablespoons garlic powder
2-4 tablespoons hot stuff --see Note 3
optional: liquid smoke, 1 to 2 tbsp

In a large bowl pour stout and add salt, whisking to dissolve salt and decarbonate the stout. Add the garlic powder and hot stuff and mix well. Put the beef strips in the marinade by handfuls, swirling around to make sure all surfaces have come in contact with the marinade. Place the beef in a nonreactive container (a stainless stockpot works fine), pour the remaining marinade over the beef, mix well, cover and refrigerate for at least an hour (more is better--overnight is fine). If you have time, mix up the beef strips every so often in the marinade.
Place the strips flat on the trays and dry to your desired amount of dryness. I prefer crisp to leathery, but do it however you want.
Note 1: Before slicing the beef, trim all extra fat off the surface of the meat. I like to use round roast because it's very lean; whenever possible, slice the strips across the grain. Slicing it with the grain results in a stringy final product. Eye of round costs a little more, but is very lean and also is very easy to slice across the grain, and that yields a less stringy product. Don't use a fatty cut of meat because it won't dry as thoroughly and won't have the storage properties of a leaner cut. (The fat can turn rancid.)
Note 2: I have found mushroom flavored soy sauce at an Asian market. It works great in this recipe.
Note 3: For the hot stuff, cayenne works well; you have to judge for yourself how hot your particular cayenne pepper is. (Mass market cayenne from brands like McCormick is relatively mild; powdered chili peppers from a Mexican or Indian market will be much hotter.) If you're unsure, go easy with the hot stuff. You can always sprinkle a little more hot stuff on the finished product if you wish. I have used chipotle powder with good results; 4 tablespoons in this recipe makes a quite hot product, and 2 tbsp makes a pleasantly zingy one. If you want something quite mild, use sweet Hungarian paprika which would make a product not at all hot but would still have a good flavor. You can also use smoked Spanish paprika ('pimenton') which comes in three degrees of hotness (sweet, bittersweet & hot). If you use that, though, or chipotle powder, don't use any additional smoke flavor. --Don't use a hot sauce that's vinegar based (like Tabasco or Sriracha)--the vinegar taste will be concentrated in the finished product.