The fix adds an entity on the map near the fence exploiters use, the entity is basically a small zone of insta-death.

This is now in effect on our servers and does not require any downloading considering it's completely server-side. Here is a demo I made to show how it works:
LINKAGEHow-To Instructions1. Download Ented
http://www.serverwiki.org/index.php/EntEd2. Make a copy of cp_badlands and store it somewhere.
3. Open cp_badlands
4. At the end of the list of entities, add:
{
"origin" "40 1816 199"
"spawnflags" "13"
"damagescale" "200"
"ignitionpoint" "32"
"firetype" "0"
"fireattack" "4"
"firesize" "128"
"health" "30"
"StartDisabled" "0"
"classname" "env_fire"
}
{
"origin" "-40 -1816 199"
"spawnflags" "13"
"damagescale" "200"
"ignitionpoint" "32"
"firetype" "0"
"fireattack" "4"
"firesize" "128"
"health" "30"
"StartDisabled" "0"
"classname" "env_fire"
}
(Yes I know TF2 doesn't really support env_fire but this is a temp fix)
5. Save and re-upload to server.
Alternate Fix - Adds a Barrel{
"origin" "40 1816 199"
"targetname" "prop_deathbarrel"
"StartDisabled" "0"
"spawnflags" "0"
"solid" "6"
"skin" "0"
"SetBodyGroup" "0"
"rendercolor" "128 128 0"
"renderamt" "150"
"RandomAnimation" "0"
"pressuredelay" "0"
"PerformanceMode" "0"
"model" "models/props_badlands/barrel0
1.mdl"
"mindxlevel" "0"
"MinAnimTime" "5"
"maxdxlevel" "0"
"MaxAnimTime" "10"
"fadescale" "1"
"fademindist" "-1"
"fademaxdist" "0"
"ExplodeRadius" "0"
"ExplodeDamage" "0"
"disableshadows" "0"
"angles" "0 90 0"
"classname" "prop_dynamic"
}
{
"origin" "-40 -1816 199"
"targetname" "prop_deathbarrel"
"StartDisabled" "0"
"spawnflags" "0"
"solid" "6"
"skin" "0"
"SetBodyGroup" "0"
"rendercolor" "128 128 0"
"renderamt" "150"
"RandomAnimation" "0"
"pressuredelay" "0"
"PerformanceMode" "0"
"model" "models/props_badlands/barrel01.mdl"
"mindxlevel" "0"
"MinAnimTime" "5"
"maxdxlevel" "0"
"MaxAnimTime" "10"
"fadescale" "1"
"fademindist" "-1"
"fademaxdist" "0"
"ExplodeRadius" "0"
"ExplodeDamage" "0"
"disableshadows" "0"
"angles" "0 90 0"
"classname" "prop_dynamic"