diff -Nur -Xfreecivdiff.ignore freeciv-cvs/server/diplomats.c freeciv-patched/server/diplomats.c
--- freeciv-cvs/server/diplomats.c	2003-07-21 13:58:27.000000000 +0100
+++ freeciv-patched/server/diplomats.c	2003-07-24 17:03:47.000000000 +0100
@@ -827,7 +827,8 @@
   - Check for infiltration success.  Our saboteur may not survive this.
   - Check for basic success.  Again, our saboteur may not survive this.
   - Determine target, given arguments and constraints.
-  - If specified, city walls and anything in a capital are 50% likely to fail.
+  - If specified, city walls and anything in a capital are 50% likely to
+    fail (with default rulesets, due to Spy_Resistant improvement effects).
   - Do sabotage!
 
   - The saboteur may be captured and executed, or escape to its home town.
@@ -838,7 +839,6 @@
   struct player *cplayer;
   int count, which, target;
   const char *prod;
-  struct city *capital;
 
   /* Fetch target city's player.  Sanity checks. */
   if (!pcity)
@@ -992,12 +992,19 @@
 
     /*
      * One last chance to get caught:
-     * If target was specified, and it is in the capital or are
-     * City Walls, then there is a 50% chance of getting caught.
+     * If target was specified, we check for any active Spy_Resistant
+     * effects (e.g. from the Palace or City Walls) which define the
+     * chance of getting caught.
      */
-    capital = find_palace (city_owner (pcity));
-    if ((pcity == capital) || (improvement == B_CITY)) {
-      if (myrand (2) == 1) {
+    if (improvement >= 0 && improvement != B_LAST) {
+      int failchance = 0;
+      impr_effects_iterate(iter, improvement, pcity, cplayer) {
+        if (iter.imeff->type == EFT_SPY_RESISTANT) {
+          failchance += iter.imeff->amount;
+        }
+      } impr_effects_iterate_end;
+
+      if (myrand(100) < failchance) {
 	/* Caught! */
 	notify_player_ex(pplayer, pcity->x, pcity->y, E_MY_DIPLOMAT_FAILED,
 			 _("Game: Your %s was caught in the attempt"