There's no way anyone able to get themselves off the ground is going to be heavy enough to break this thing. And it's not that small. 5-6 inches long. So you should be fine. A bigger concern is that you'll yank your belayer off the ground. Also troubling is the term "toprope lead fall". That's an oxymoron. Be careful.To add to this, remember to use ropes in the proper diameter range of 10mm to 13mm, and you can also anchor your belayer in to the ground so that way there is no concern about your top rope belayer holding you. Gri gri's are almost fool proof, and only malfunction with user error, so be sure you know how to use it safely first!Becareful though, This is not suppose to be given to an unexperienced belay. It has and can get people hurt. Its easy to use but not fool proof. I use grigris alot!!! and I wouldn't say that they ONLY fail with user error, but EXTREMELY rarely. If used properly it is no safer than an atc and MUCH more expensive. It has it's place and does it's job well when used properly, but I have found that it tends to lead to a false sense of security and a an unattentive belayer sometimes. Like I said I use grigris alot in one particular application, but for traditional belay situations i still prefer tube style belay devices. Just like any other belay device when used properly the size of the climber really does not factor into the stopping ability, with the grigri however it CAN affect how smoothly it releases. Also if you do choose the grigri make sure you use at least 10mm or larger rope and keep the device CLEAN, dirt in the wrong place can cause it to stick in the wrong position.

I've never heard of dynamic rope being sold by the foot. Most are sold in 50, 60, or 70m lengths, which is what outdoor routes are geared toward anyway. Maybe if you explained what you wanted it for I could help more....my first rope was gym rope. It was 30 meters (about 100ft) of dynamic 9.8mm and who knows what brand. A climbing gym near you might be able to hook you up.There are probably "challenge courses" in your area... a local course probably won't sell you rope, but they should be able to tell you who the nearest vendors are and they would probably sell you rope by the foot. But most likely it will be 10.5-11mm stuff and the heaviest toughest stuff they can find. And some vendors shy away from dealing with the public, but... that's the only way I know to buy dynamic rope buy the foot.