Hi Lance. Just have to ask, where is Lager des Adlers? Sounds kinda cool.
Anyway, I'll tell you right up front I'm sort of a cheap S.O.B. so I like to either use a natural backstop or make my own. Here are a couple of options for you.
Depending on your soil to rock ratio where you live, there is nothing more durable than a dirt bank. Here in this part of Missouri, there isn't much rock until you actually get into a hill side. In the river bottoms where I hunt rocks are nearly nonexistent. The levee that follows the river is a great natural backstop. When at home a small dirt bank on the curve of my driveway is where I do all my practice shooting.
Since you probably don't have that option if you have lots of rocks, if you want a permanent target you can make a similar setup with some landscape timbers and a couple loads of sand, peat moss, potting soil or just plain dirt with the rocks picked out.
If THAT isn't an option you will be stuck with either a self made or commercial target stop. If you have any sort of factory in your area, you can check with them to see if they have any sort of plastic sheeting, plastic bags or plastic wrap that ends up as waste and you could make a home made "you stuff it" type target. Where I work, we bottle spices (Lawrys brand) and we get certain size spice bottles in large plastic bags about 5 X 5 feet. In a single shift they empty hundreds of these bags and they use one of the empties to stuff all the rest into for disposal. I take one and add 2 or three bags to the outside from opposite directions (put a full bag into an empty bag open end first several times over) so nothing will fall out and I have a great target that will hold up in all kinds of weather and will stop any arrow.
Another option is the plastic shrink wrap used to hold pallets of goods together. It's like plastic wrap used for food. You could go to almost any store that gets pallets of goods shipped in and they probably have a dumpster full of plastic shrink wrap after they get a shipment in. Lawn and feed stores are great too! The plastic "burlap" type bags they get seed in make a great self stuff target and a 100 pound seed bag is about the size of a deers torso too! Stuff it with anything from rags and old pillow filling to plastic wrap or more of the plastic bags like used for the outside. The tighter you stuff it, the better it will stop an arrow but at some point, it gets harder to pull the arrow out. Of course, a broadhead is harder to pull out than a field point and you always have to be careful when pulling out broadheads from any target.
Another scrounger type material is ethafoam. It's like white (usually, I've seen black and grey in industrial use) styrofoam only it's plastic and has a texture similar to a sponge but very firm. It is actually used in some comercially made targets but sometimes you can find a supply of it for free from a factory.
Well, I could go on and list several more options for do it yourself type backstops but I think yo get the idea. Look around a bit and see what is available in your area. You migt be suprised.