Cheapest priced copy (Planeshift): $0.35 at Card Kingdom, near mint, their price list as of .
Guard Dogs 
Creature — Dog · 2/2 · Uncommon · Planeshift · #5
{2}{W}, {T}: Choose a permanent you control. Prevent all combat damage target creature would deal this turn if it shares a color with that permanent.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $0.35 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Planeshift | 5 | Uncommon | $0.35 | $0.99 |
2 rulings from Wizards of the Coast
- 4 October 2004You only check colors on resolution and not later when the damage prevention actually is applied.
- 4 October 2004You choose the target on activation and choose the permanent which is compared for color on resolution.