The Shulchan Aruch (451:6) discusses the use of inserting a hot stone into a large pot of boiling water to complete the hagala process. Aside from the 'border-lip' option mentioned in the Shulchan Aruch, are there alternative practical (halachically acceptable) options to sticking a fiery hot stone/brick into a boiling pot of water?
There are a couple of practical ways of accomplishing the "hot stone" trick without actually using hot stones (btw heating up stones can cause moisture inside to expand and the stone can literally explode. I know a mashgiach who was very seriously hurt when it happened.)
1) Dayan Yisroel Y. Fisher used a clothing iron to "iron" the water of his countertop, to effect the "hot stone" treatment. Make sure the iron is a steam iron and waterproof. Depending on the surface that you're using this is an extremely practical option. (I heard this from a few rabbonim in Yerushalayim, I think it's brought in Halichos Yisroel on pesach.)
2) We posken (O.C. 451 at the beginning; I think sif 4-5) that libun kal is just as good (even better in fact) than hagalah. So you could kasher the whole pot with hagalah, and then (after emptying the water) doing libun kal on the lip of the pot. Hold the pot upside down over a burner. Slowly rotate the pot back and forth. You don't want to have one section for too long over the fire, because it can ruin the pot. But you want the pot lip to slowly get heated up. (I've found that doing a third of the pot lip at a time is practical. You can rotate enough so it's not too much in the fire, yet it's a small enough area that it doesn't cool down too much.)
While you have the pot over the fire, put a piece of tissue on the inside of the pot opposite the fire. When the tissue starts to catch on fire (turning brown is good enough- it doesn't need to burst into flames) then you know that section is done.
3) I found this works very well: take a short section of thick metal pipe (not thin aluminum). Stick a metal hanger through it, then bend the hanger back and attach the ends together. You'll end up with a handle to hold the hanger, and the piece of metal rolling freely around the middle of the hanger.
Then you take the piece of metal, hold it over a fire until it's super hot, and you can use it as a hot stone. You can roll it over the edges of the pot while pouring boiling water over it. This also works well for counters etc. Every 15-30 seconds you stick it back over the fire to get hot again. It's very easy and pretty safe.
After looking into the question more, it seems the poskim at Dinonline allows this alternative to hot bricks/stones:
You can also pour boiling water (from a kettle or hot water heater) into the center of the pot and have the water spill over the edges.
Though I don't know if other kashrus agencies disagree since the major agencies I've read thus far don't mention this alternative. (STAR-K, OU, cRc - the latter mentions calling your Rav if the pot is too large, so perhaps they have alternatives too)