Most people will experience the itchy rash of poison ivy at some time.For those especially sensitive to the weed, there's a way to prevent that nasty reaction before you are exposed in the woods. Trail signs mark the "safe" places to walk at the Runge Nature Center."If you get off the trails you had better know what it looks like because there's as lot of it around this year," warns manager Kathy Cavender.She's talking about poison ivy. A bumper crop means you have a good chance of getting the itchy rash, even if you aren't the one touching it. "Keep in mind that if your dog came out and came into contact with it and got the oil on its coat, and you pet the dog, you can get poison ivy that way as well," warns Cavender.So how can you be safe?The answer may come in a poison ivy containing solution mixed at a Jefferson City pharmacy. A liquid much like this is diluted until it's clear. You put the homeopathic drops called Rhus-Tox under your tongue to build up an immunity to the toxin. Unlike a vaccine used for diseases like tetanus or the measles, the immunity does not last. You start by putting the drops under your tongue once a week for three weeks, then use it once a month to stay protected.Dr George Carr of the Jefferson City Medical Group has seen it work. "We have a lot of people who claim they don't get poison ivy while they're using it. Others claim that it's not as bad if they do get it, it's a milder case," says Carr. You need a prescription for the drops. For a little more than $30 you can get a seven month supply. Rhus-Tox is sold on the internet in different forms, but Dr. Carr says he doesn't trust it."It's available out there, it's simply people who have taken poison ivy leaves and made this extract out of it. I feel a lot more comfortable and a lot safer using a compounding pharmacy because I know exactly what the concentration is," warns Carr.Cavender says she would like to check it out, but for now she feels safer knowing what to watch out for when she's in the woods.